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  • Electronic Resource  (666,089)
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  • 1995-1999  (640,711)
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  • 1
    Electronic Resource
    Electronic Resource
    A measurement of τ polarization in Z^0 decays (1992-8977)
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    Details
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(92)91549-O
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Measurement of the average lifetime of b hadrons (1993-4325)
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    Details
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(93)91027-K
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  • 3
    Book
    Book
    Computing : archives for informatics and numerical computation; Supplementum (1977-2003)
    Wien [u.a.] :Springer, ; 1.1977 - 16.2003; damit Ersch. eingest.
    Details
    Title: Computing : archives for informatics and numerical computation; Supplementum
    Publisher: Wien [u.a.] :Springer,
    Year of publication: 1977-2003
    Dates of Publication: 1.1977 - 16.2003; damit Ersch. eingest.
    Type of Medium: Book
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    ZIB Catalog
    Zuse Institute Berlin get availability status
  • 4
    Electronic Resource
    Electronic Resource
    Property calculations using perturbed orbitals via state-specific multireference coupled-cluster and perturbation theories (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3820-3831 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we apply the recently developed state-specific multireference coupled-cluster and perturbation theories to calculate electrical properties such as dipole moment and static polarizability using perturbed orbitals in finite fields. The theories are built on complete active space reference functions, and are designed to treat quasidegeneracy of varying degrees while bypassing the intruder problem. Numerical results are presented for the model systems H4 with trapezoidal geometry and the lowest two singlet states of CH2. Both the systems require a multireference formulation due to quasidegeneracy. In the field-free situation, the former encounters intruders at an intermediate trapezoidal geometry in the traditional treatment using effective Hamiltonians, while the latter shows a pronounced multireference character in the two singlet states. This affects the response properties in the presence of a perturbing field. A comparison with the full CI results in the same basis indicates the efficacy of the state-specific methods in wide ranges of geometries, even when the traditional effective Hamiltonian based methods fail due to intruders. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479685
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  • 5
    Electronic Resource
    Electronic Resource
    Interaction optimized basis sets for correlated ab initio calculations on the water dimer (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3812-3819 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A compact basis set is constructed for the water dimer by focusing directly on an optimal description of the counterpoise-corrected interaction energy (ΔE) rather than on the total energy of the fragments. The optimization criterion is that the basis set should be of uniform accuracy, i.e., the truncation error in ΔE due to the basis set incompleteness should be the same for all symmetry types at all sites. Aiming at a truncation error of 10 μhartree per symmetry at the SCF+MP2 (self-consistent field+Møller–Plesset second-order) frozen core level the resulting interaction optimized basis set comprises 249 functions. The composition of this IO249 set is O/5s3p4d3f2g1h, H(donor)/2s4p1d, H(else)/2s3p, bond function set/3s3p2d1f. An all-electron variant, IO275, is described as well. A recipe to obtain interaction optimized sets for other systems is given. The set IO249 yields a ΔE(fc) value at the Feller–Frisch geometry of −4.87 kcal/mol. Of the many orbital-based calculations that have been reported for this system only Schütz' 1046-function calculation [J. Chem. Phys. 107, 4597 (1997)] was more accurate. The small size of the interaction optimized sets opens the possibility for high-accuracy SCF+MP2 work on larger systems than have been accessible before. It also brings higher-level correlated treatments within reach. An Appendix summarizes two additivity rules which allow the ΔE for a larger basis set to be estimated to very high accuracy from the results of smaller basis sets. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479684
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  • 6
    Electronic Resource
    Electronic Resource
    Z-vector formalism for the Fock space multireference coupled cluster method: Elimination of the response of the highest valence sector amplitudes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3832-3836 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we present Z-vector formalism for the Fock space multireference coupled cluster framework. We present detailed equations describing the derivative effective Hamiltonian, where the response amplitudes of the highest Fock sector are eliminated. We discuss the conditions and approximations under which the formalism is possible. We also discuss the implications and comparison with the similar formalism in the single reference framework. The computational advantages and feasibility are also commented upon in this paper. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479686
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic ground state of iron(II) porphine. II (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3837-3845 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ten low-lying electronic states of Fe(II) porphine, 5A1g, 5Eg, 5B2g, 3A2g, 3B2g, 3Eg(A), 3Eg(B), 1A1g, 1B2g, and 1Eg states, are studied with multiconfigurational second-order perturbation (CASPT2) calculations with complete active space self-consistent field (CASSCF) reference functions with larger active space and basis sets. The enlargement of active space and basis sets has no influence on the conclusion of a previous multireference Møller–Plesset perturbation (MRMP) study. The present CASPT2 calculation concludes that the 5A1g state is the ground state. A relativistic correction has been performed by the relativistic scheme of eliminating small components (RESC). For energetics, no significant contribution from the relativistic correction was found. The relative energies and orbital energies are not changed appreciably by the introduction of a relativistic correction. The present result does not agree with all the spectroscopic observations, but is consistent with a magnetic moment study. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479687
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  • 8
    Electronic Resource
    Electronic Resource
    High-level ab initio computations of structures and relative energies of two isomers of the CO2 trimer (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3846-3854 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The two-body interaction energies of the cyclic (C3h) and noncyclic (C2) trimers at the basis set limit (15.55 and 16.55 kJ/mol) were estimated by means of second-order Møller–Plesset perturbation theory including terms linear in the interelectronic distance (MP2-R12 approach). Coupled cluster calculations with single and double substitutions and with noniterative triple excitations [CCSD(T)] were carried out to correct the MP2-R12 two-body interaction energies for the effect of higher excitations, and also for the evaluation of the three-body interaction energies. The calculated bonding energies of the trimers using this model calculation (16.82 and 17.20 kJ/mol) suggest that the two isomers are nearly isoenergetic. The three-body terms are small (only of the order of 1 kJ/mol), stabilizing the cyclic trimer, but destabilizing the noncyclic trimer. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479688
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  • 9
    Electronic Resource
    Electronic Resource
    Density functional theory study on ethanol dimers and cyclic ethanol trimers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3855-3861 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and the relative stability of the ethanol dimer and the cyclic ethanol trimer were studied using density functional theory methods. The geometries of the different dimers and trimers were optimized at the B3LYP/6-311+G(d,p) level of theory, while the final energies were obtained at the B3LYP/6-311+G(3df,2p) level. Four different (ethanol)2 complexes were found to be local minima of the potential energy surface, the global minimum being that in which both monomers exhibit a trans conformation. The hydrogen bond (HB) in ethanol dimer is slightly stronger than in methanol dimer, reflecting the enhanced intrinsic basicity of ethanol with regards to methanol. The OH donor stretch appears redshifted by 161 cm−1, while the redshifting undergone by the OH acceptor stretch is negligibly small. The relative stability of the trimers is a function of the number of monomers with a gauche conformation, the global minimum being that in which the three monomers have a trans conformation. As for water and methanol trimers, the three HBs in the cyclic ethanol trimer are not strictly equivalent. Consistently, the redshiftings of the OH stretching frequencies are different. Cooperative effects are sizably large, as reflected in the O(centered ellipsis)O distances, the elongation of the OH donor groups, the charge density at the bond critical points, the frequency shiftings of the OH stretches, and the additivity interaction energy. The most significant features of the vibrational spectra of the monomers, the dimers, and the trimers in the 800–1200 cm−1 region are reasonably well reproduced by our calculations.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479689
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamics of the O(3P)+HCl reaction on the 3A″ electronic state: A new ab initio potential energy surface, quasi-classical trajectory study, and comparison to experiment (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3862-3873 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new potential energy surface for the lowest 3A″ electronic state of the O(3P)+HCl system is presented. This surface is based on electronic energies calculated at the multireference configuration interaction level of theory with the Davidson correction (MR-CI+Q) using the Dunning cc-pVTZ one-electron basis sets. The ab initio energies thus obtained are scaled using the scaled external correlation (SEC) method of Brown and Truhlar. The SEC-scaled energies are fitted to a simple analytical expression to yield a potential energy surface which correlates the reactants O(3P)+HCl(1Σ+) to the products OH(2Π)+Cl(2P). The reaction barrier on this surface lies at an O–H–Cl angle of 131.4° at an energy of 9.78 kcal/mol above the asymptotic O+HCl minimum. This barrier is 1.3 kcal/mol higher than that on the potential energy surface obtained by Koizumi, Schatz, and Gordon (KSG) [J. Chem. Phys. 95, 6421 (1991)] and 1.1 kcal/mol lower than the S2 surface of Ramachandran, Senekowitsch, and Wyatt (RSW) [J. Mol. Struct. (Theochem) 454, 307 (1998)]. The dynamics of the reaction O(3P)+HCl(v=2; j=1,6,9)→OH(v′,j′)+Cl on this potential surface is studied using quasi-classical trajectory (QCT) propagation and the results are compared to the experimental observations of Zhang et al. [R. Zhang, W. J. van der Zande, M. J. Bronikowski, and R. N. Zare, J. Chem. Phys. 94, 2704 (1991)]. The broad distribution of collision energies in the experiment is modeled by computing weighted averages of the quantities of interest with the weighting factor at each collision energy determined by the collision energy distribution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480264
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  • 11
    Electronic Resource
    Electronic Resource
    Liquid vapor equilibria for an ab initio model for water (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2103-2108 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vapor–liquid coexistence densities for water near the critical point were determined using a polarizable ab initio based model and grand canonical Monte Carlo simulations combined with the histogram reweighting technique. The predictions of the model used, which is found to give good agreement with experimental data at ambient conditions, are far below the experimental critical temperature and density. The saturation pressure is also overestimated. The source of this discrepancy may be related to the high pressure that the model exhibits even for liquid water. Since there is no fitting to experimental data, it is possible to refine the potential in a systematic way. In particular, an improvement in the sampling of the ab initio calculation for the repulsive part of the intermolecular potential is suggested in order to obtain better agreement with experiment at high temperatures and pressures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479479
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  • 12
    Electronic Resource
    Electronic Resource
    Modeling of zeolite L crystallization using continuum time Monte Carlo simulations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2143-2150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model to investigate a gel-to-zeolite transformation as a possible growth mechanism through association and rearrangements of extended precursor structures is developed and solved via continuum time lattice Monte Carlo simulations. The model is used to study the morphology of zeolite L nanocrystals grown from an initial amorphous microporous precursor gel. The model considers gel dissolution to release growth precursor extended structures, precursor migration, precursor–precursor association, precursor incorporation into zeolite nanoparticles, and zeolite dissolution. It is shown that the gel-to-zeolite transformation can occur when dissolved precursor migration is slow compared to precursor incorporation and zeolite dissolution. Under these conditions, the initial gel microstructure (intraparticle porosity) has a significant effect on the zeolite morphology and on the crystallization kinetics. This transformation proceeds in two stages: A zeolitic framework forms initially without long-range order, followed by slow rearrangement of building units into nanocrystalline particles with possible defects. Finally different growth modes are identified as a function of microkinetic parameters and gel morphology. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479484
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  • 13
    Electronic Resource
    Electronic Resource
    Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2157-2163 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of tris(8-hydroxyquinoline) aluminum (Alq3) has been studied in the pristine molecular solid state as well as upon interaction (doping) with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq3 molecule, resulting in a new spectral feature (peak) in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq3 molecule. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479486
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  • 14
    Electronic Resource
    Electronic Resource
    Hard core Yukawa fluid with temperature and density dependent interaction: Phase diagram of the AOT/water/decane microemulsion (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2151-2156 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A fluid with an interaction potential consisting of a hard core and an attractive Yukawa tail is considered. The strength of the attraction is taken to depend both on density and temperature in order to take into account the state dependence of the effective interaction suggested by the analysis of structural data of several colloidal suspensions, in particular microemulsions of AOT reverse micelles. The thermodynamics of this fluid is investigated starting from the inverse temperature expansion of the free energy in the mean spherical approximation. The temperature and density dependence of the interaction is incorporated in consistent expressions for the pressure, isothermal compressibility, and chemical potential. The phase diagram predicted by this method is in agreement with experimental data on AOT reverse micelles analyzed in the effective one component approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479485
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  • 15
    Electronic Resource
    Electronic Resource
    Melting thermodynamics of organic nanocrystals (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2176-2180 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The size-dependent melting temperature and the size-dependent melting entropy of organic nanocrystals are predicted by use of our simple model being free of any adjustable parameter. The model predictions for the size-dependent melting temperature and the size-dependent melting entropy are supported by the experimental results on benzene, chlorobenzene, heptane, and naphthalene nanocrystals. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479489
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  • 16
    Electronic Resource
    Electronic Resource
    Oxygen adsorption on Ag(111): X-ray photoelectron spectroscopy (XPS), angular dependent x-ray photoelectron spectroscopy (ADXPS) and temperature-programmed desorption (TPD) studies (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2169-2175 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The O2 adsorption on Ag(111) single crystal in the range of 300–500 K has been studied by XPS, ADXPS, and TPD. At room temperature, the O1s line observed at 530.0 eV goes down to 528.2 eV when the sample is heated to 420 K. The comparison of XPS and TPD data indicates that both lines can be assigned to chemisorbed atomic oxygen. The depth concentration profiles calculated on the basis of the angular-dependent XPS data show that the line at 530.0 eV is responsible for oxygen adsorbed at the surface, as opposed to that at 528.2 eV which is assigned to oxygen between the top and second silver layers. The formation of surface silver oxide is concluded in the latter case. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479488
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  • 17
    Electronic Resource
    Electronic Resource
    The structure of the liquid-vapor interface of a gallium-tin binary alloy (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2181-2189 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of self-consistent quantum Monte Carlo simulations of the structure of the liquid-vapor interface of the alloy Sn0.09Ga0.81. Our calculations are in very good agreement with the experimental results reported by Lei, Huang and Rice [J. Chem. Phys. 107, 4051 (1997)]. In particular, our calculations confirm the experimentally inferred existence of a partial second layer of Sn below the complete outermost layer of Sn in the stratified liquid-vapor interface of this alloy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479490
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  • 18
    Electronic Resource
    Electronic Resource
    The semirigid vibrating rotor target model for quantum polyatomic reaction dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3929-3939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we present detailed quantum treatment of the semirigid vibrating rotor target (SVRT) model for reaction dynamics involving polyatomic molecules. In the SVRT model, the reacting (target) molecule is treated as a semirigid vibrating rotor which can be considered as a three-dimensional generalization of the diatomic molecule. This model provides a realistic framework to treat reaction dynamics of polyatomic systems. Using the SVRT model, it becomes computationally practical to carry out quantitatively accurate quantum dynamics calculation for a variety of dynamics problems in which the reacting molecule is a polyatomic or complex molecule. In this work, specific theoretical treatment and mathematical formulation of the SVRT model are presented for three general classes of reaction systems: (1) reaction of an atom with a polyatomic molecule (atom–polyatom reaction), (2) reaction between two polyatomic molecules (polyatom–polyatom reaction), and (3) polyatomic reaction with a rigid surface (polyatom–surface reaction). Since the number of dynamical degrees of freedom in the SVRT model for the above three classes of dynamical problems is limited, accurate quantum (both ab initio and dynamical) calculations are possible for many reactions of practical chemical interest. In this paper, a time-dependent wave packet approach is employed to implement the SVRT model for dynamics calculation of polyatomic reactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479696
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  • 19
    Electronic Resource
    Electronic Resource
    Fourier transform microwave rotational spectra of the Ne2–N2O and Ar2–N2O van der Waals trimers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3919-3928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A pulsed molecular beam cavity Fourier transform microwave spectrometer was used to measure pure rotational spectra of nine isotopomers of Ne2–N2O, and of three isotopomers of the Ar2–N2O van der Waals trimer. For Ne2–N2O, these are 20Ne20Ne–14N14N16O, 20Ne22Ne–14N14N16O, 22Ne22Ne–14N14N16O, 20Ne20Ne–15N14N16O, 20Ne22Ne–15N14N16O, 22Ne22Ne–15N14N16O, 20Ne20Ne–14N15N16O, 20Ne22Ne–14N15N16O, and 22Ne22Ne–14N15N16O. Those for Ar2–N2O are 40Ar40Ar–14N14N16O, 40Ar40Ar–15N14N16O, and 40Ar40Ar–14N15N16O. The spectra were measured in the frequency range between 3 and 18 GHz. Both a- and c-type transitions were measured for all Ne2–N2O isotopomers. In the case of the mixed, 20Ne22Ne containing, isotopomers a small b-dipole moment occurs and two b-type transitions were measured. In the spectra of Ar2–N2O only b- and c-type transitions were measured. Rotational and centrifugal distortion constants were determined for all the isotopomers of each complex. The spectral analyses show that Ne2–N2O is a highly asymmetric prolate rotor (κ=−0.158 for 20Ne20Ne–14N14N16O) while Ar2–N2O is a highly asymmetric oblate rotor (κ=0.285 for 40Ar40Ar–14N14N16O). Both trimers were found to have distorted tetrahedral structures with the rare gases tilted towards the O atom of the N2O subunit. Nuclear quadrupole hyperfine structures due to both terminal and central 14N nuclei were observed and analyzed to give the nuclear quadrupole coupling constants, χaa(1), χbb(1) and χaa(2), χbb(2). The resulting spectroscopic constants were utilized to derive ground state effective structures, ground state average structures, and partial substitution structures. Harmonic force field analyses were performed for each complex using the obtained quartic centrifugal distortion constants. The results of the spectroscopic analyses are discussed in the light of possible three-body nonadditive interactions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479695
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  • 20
    Electronic Resource
    Electronic Resource
    Photodissociation of hydrogen sulfide at 157.6 nm: Observation of SH bimodal rotational distribution (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3940-3945 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of the H2S molecule at 157.6 nm was studied experimentally using the Rydberg tagging technique. Translational energy distributions of the H-atom product from the H2S photodissociation were measured, and the SH(X 2Π)+H(2S) channel was found to be the dominant dissociation process. Spin-orbit and rovibrational state distributions were also obtained for the SH product, which was found to be both vibrationally and rotationally excited. An intriguing bimodal rotational distribution in the lowest two vibrational states, v=0 and 1, has been clearly observed for the SH product, indicating that there are two distinctive dissociation mechanisms involved in the photodissociation of H2S at 157 nm excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479736
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  • 21
    Electronic Resource
    Electronic Resource
    Hydrogen bond and cooperative effect in the reactions of HOCl with HCl on water clusters (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2242-2254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reactions of HOCl with HCl on water clusters have been theoretically investigated. Ab initio calculations indicate that hydrogen bond and cooperative effect play an essential role in the reactions; that the reaction barrier of HOCl with cyclic (H2O)n.HCl cluster is the least at n=3 and that the ionization of HCl and HOCl on ice surfaces may not be complete but partly at very low temperatures. Two cases a and b of the model reactions are considered for detailed analysis. On the surface of ice, the barrier energies are about 4 and 6 kcal/mol for cases a and b, respectively, at the MP2//HF/6-31G(d) level, which is close to an experimental estimation. This study suggests a similar previously reported mechanism that the heterogeneous reaction of HOCl with HCl on ice is catalyzed at the stratospheric conditions through structure catalysis and hydration that enhances ion character of species. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479565
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  • 22
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    Electronic Resource
    Physical aging by periodic creep and interrupted creep experiments (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2235-2241 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A newly developed "interrupted creep" experiment has been used to study the physical aging of a low molecular weight polystyrene, Tg∼69 °C. The results of the new experiment are compared to those obtained from traditional "periodic creep" experiments. The interrupted creep experiment provides information about the viscosity, the recoverable creep compliance and the steady-state compliance, Js, during aging. Low molecular weight polystyrene was chosen because it exhibits a steady-state compliance that is a strong function of temperature. Aging was conducted at three temperatures, 68.2, 65.7 and 61.0 °C, using both down-jump and up-jump experiments. The behavior observed in the new experiments mirrors the behavior observed in the traditional experiments. In addition, the new experiments allow the first ever determination of how Js evolves during aging. The change of Js with aging time was calculated using the relationship between the shift factors, obtained from the recoverable creep compliance data, and the average relaxation times, obtained from the viscosity. The advantage of the new experiment is that it provides both the short-time recoverable creep compliance information and the long-time viscous flow. By combining these contributions to the creep compliance in a simple additive fashion, one can obtain a more complete picture of how the material is behaving during aging. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479495
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  • 23
    Electronic Resource
    Electronic Resource
    Phase separation of polymer blend films near patterned surfaces (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2259-2269 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of a patterned surface on the phase separation kinetics of a thin polymer film has been investigated using the Cahn–Hilliard–Cook model in three dimensions with the addition of a short range surface potential. We have observed pattern-induced spinodal waves perpendicular to the surface creating "checkerboard"-like composition fluctuations for a wide range of patterns used in this study. The number of such layers strongly depends on the magnitude of the thermal noise. For sufficiently thin films, where the film thickness is smaller than the spinodal wavelength, spinodal decomposition can be arrested if the surface potential and the characteristic size of the pattern are chosen accordingly, enabling the transfer of surface patterns to the film material. The kinetic pathways through which the equilibrium states are reached delicately depend on the particular pattern, its size, and the film thickness. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479497
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  • 24
    Electronic Resource
    Electronic Resource
    Spin–orbit effects in quantum mechanical rate constant calculations for the F+H2→HF+H reaction (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4013-4024 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Exact and approximate quantum mechanical calculations of reaction probabilities and cumulative reaction probabilities have been carried out for the F+H2 reaction on the ab initio adiabatic potential energy surfaces by Stark and Werner (SW) and by Hartke, Stark, and Werner (HSW), the latter including spin–orbit corrections in the entrance channel. These data have been employed to obtain thermal rate constants for the title reaction in the temperature range 200–700 K. The exact and approximate results have been compared with experimental determinations and previous theoretical predictions. In particular, the reaction probabilities obtained on the HSW surface are found to be in very good agreement with recent calculations by Alexander et al. [J. Chem. Phys. 109, 5710 (1998)] based on the exact treatment of spin–orbit and Coriolis coupling for this system. However, the rate constants calculated on the HSW PES are systematically lower than the experimental values, which indicates that the height of the adiabatic potential energy surface is too high. Furthermore, an estimate of cross sections from the reaction probabilities calculated by Alexander et al. shows that the contribution to the low temperature rate constants from spin–orbit excited F(2P1/2) atoms through nonadiabatic channels is very small and, thus, nonadiabatic effects are not sufficient to bring the calculated rate constants to a better agreement with the experimental measurements. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479703
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  • 25
    Electronic Resource
    Electronic Resource
    New empirical rate expression for reactions without a barrier: Analysis of the reaction of CN with O2 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4068-4076 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate coefficients of reactions that occur on potential energy surfaces without a barrier often exhibit a negative temperature dependence at low temperatures. Generally, this behavior is modeled with either the Harcourt–Essen equation, k(T)=AT−m, or a "negative" activation energy, k(T)=ATm exp{ΔE/kBT}. Neither of these expressions is consistent with the Wigner threshold law. The general expression k(T)=(1+T/TW)−m∑l=0∞Al(1+T/TW)−l(T/TW)l is proposed where the relative angular momentum of the reacting species is l, TW and m are independent parameters to be extracted from the data, and the amplitude of each partial wave is Al. This expression may be approximated by k(T)=A0(1+T/TW)−m exp[(T/TW)/(1+T/TW)]. For CN+O2→ NCO+O and CO+NO the above expression reproduces the rate data, the branching ratio to the CO+NO channel, and the reactive cross section for the NCO+O channel. The rate coefficient for the NCO+O channel is given by k(cm3 s−1)=1.79×10−10(+T/21.7)−1.38{exp[(T/21.7)/(1+T/21.7)]−1}+4.62×10−12 exp[(T/21.7)/(1+T/21.7)] while for CO+NO we obtain k(cm3 s−1)=1.79×10−10(1+T/21.7)−1.38. An analytic form of the C–O bonding potential and the electric dipole–quadrupole interaction is used to show that the quantum threshold region extends up to 7 K. These results demonstrate the need of a complete quantum treatment for reactions that proceed on potential surfaces without a barrier. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479183
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  • 26
    Electronic Resource
    Electronic Resource
    Resonant two-photon ionization spectroscopy of jet-cooled PdC (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4077-4086 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first optical investigation of the spectra of diatomic PdC has revealed that the ground state has Ω=0+, with a bond length of r0=1.712 Å. The Hund's case (a) nature of this state could not be unambiguously determined from the experimental data, but dispersed fluorescence studies to be reported in a separate publication, in combination with a comparison to theoretical calculations, demonstrate that it is the 2δ4 12σ2, 1Σ0++ state, which undergoes spin–orbit mixing with a low-lying 2δ4 12σ1 6π1, 3Π0+ state. An excited 3Σ+ state with re=1.754±0.003 Å (r0=1.758±0.002 Å) and ΔG1/2=794 cm−1 is found at T0=17 867 cm−1. Although only the Ω=1 component of this state is directly observed, the large hyperfine splitting of this state for the 105Pd 12C isotopomer implies that an unpaired electron occupies an orbital that is primarily of 5s character on Pd. Comparison to ab initio calculations identifies this state as 2δ4 12σ1 13σ1, 3Σ1+. To higher wavenumbers a number of transitions to states with Ω=0+ have been observed and rotationally analyzed. Two groups of these have been organized into band systems, despite the clear presence of homogeneous perturbations between states with Ω=0+ in the region between 22 000 and 26 000 cm−1. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479735
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  • 27
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    Electronic Resource
    An intramolecular theory of the mass-independent isotope effect for ozone. I (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4087-4100 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An intramolecular theory of the unusual mass-independent isotope effect for ozone formation and dissociation is described. The experiments include the enrichment factor, its dependence on the ambient pressure, the ratio of the formation rates of symmetric and asymmetric ozone isotopomers, the enrichment of ozone formed from heavily enriched oxygen isotopes, the comparison of that enrichment to that when the heavy isotopes are present in trace amounts, the isotopic exchange rate constant, and the large mass-dependent effect when individual rate constants are measured, in contrast with the mass-independent effect observed for scrambled mixtures. To explain the results it is suggested that apart from the usual symmetry number ratio of a factor of 2, the asymmetric ozone isotopomers have a larger density of reactive (coupled) quantum states, compared with that for the symmetric isotopomers (about 10%), due to being more "RRKM-like" (Rice–Ramsperger–Kessel–Marcus): Symmetry restricts the number of intramolecular resonances and coupling terms in the Hamiltonian which are responsible for making the motion increasingly chaotic and, thereby, increasingly statistical. As a result the behavior occurs regardless of whether the nuclei are bosons (16O, 18O) or fermions (17O). Two alternative mechanisms are also considered, one invoking excited electronic states and the other invoking symmetry control in the entrance channel. Arguments against each are given. An expression is given relating the mass-independent rates of the scrambled systems to the mass-dependent rates of the unscrambled ones, and the role played by a partitioning term in the latter is described. Different definitions for the enrichment factor for heavily enriched isotopic systems are also considered. In the present paper attention is focused on setting up theoretical expressions and discussing relationships. They provide a basis for future detailed calculations. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.480267
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  • 28
    Electronic Resource
    Electronic Resource
    Simulation of an asymmetric electrolyte with charge asymmetry 60:1 using hard-sphere and soft-sphere models (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4300-4309 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Thermodynamic and structural properties of an asymmetric electrolyte containing macroions with 60 elementary charges and monovalent counterions in aqueous solution at different concentrations have been studied by means of Monte Carlo (MC) simulations and molecular dynamics (MD) employing two different short-range potentials. The long-range Coulombic interactions were handled by using Ewald summation and the MC simulations were accelerated by a cluster-move technique, which was found to be two orders of magnitude more efficient for this system than the standard MC method. An effective repulsion was found to operate between the macroions at all concentrations. The electrostatic screening of the macroion repulsion by the counterions was stronger in the hard-sphere model as compared to a soft-sphere model. The origin of this difference arises primarily from the deeper macroion–ion potential in the former model. The results of the hard-sphere model have been compared with different more approximate theories such as the cell model solved by MC simulations, the cell model solved by the Poisson–Boltzmann (PB) equation, and the Derjaguin–Landau–Vervey–Overbeek (DLVO) theory. We have found that the cell model solved by MC simulations and combined with a charge renormalization approach is superior to the other simplified approaches and its predictions are in excellent agreement with the exact simulation results. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479728
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  • 29
    Electronic Resource
    Electronic Resource
    Nematic-isotropic interfaces in semiflexible polymer blends (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4334-4342 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present calculations of the anisotropy of the tension of interfaces separating an isotropic phase rich in a flexible polymer from a nematic phase rich in a semiflexible polymer. We find that the interfacial tension is always lower when the director is parallel to the plane of the interface than when it is perpendicular. The ratio of the tension in the perpendicular to parallel case can be quite large, of order 5 or so, depending on the strength of the nematic interactions. We also find that the interfacial width is always lower in the parallel case even though the tension is lower; this is because the orientational density prefers parallel alignment of chains at the interface. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479732
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  • 30
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    Electronic Resource
    Numerical prediction of the melting curve of n-octane (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1501-1510 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We compute the melting curve of n-octane using Molecular Dynamics simulations with a realistic all-atom molecular model. Thermodynamic integration methods are used to calculate the free energy of the system in both the crystalline solid and isotropic liquid phases. The Gibbs–Duhem integration procedure is used to calculate the melting curve, starting with an initial point obtained from the free energy calculations. The calculations yield quantitatively accurate results: in the pressure range of 0–100 MPa, the calculated melting curve deviates by only 3 K from the experimental curve. This deviation falls just within the range of uncertainty of the calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479409
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  • 31
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    Electronic Resource
    Pulse sequence symmetries in the nuclear magnetic resonance of spinning solids: Application to heteronuclear decoupling (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1511-1519 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop the average Hamiltonian theory of a class of symmetrical radio-frequency pulse sequences in the NMR of rotating solids. Theorems are presented which allow one to predict the elimination of many average Hamiltonian terms, without detailed calculation. These results are applied to the problem of heteronuclear decoupling in the presence of rapid magic angle spinning. We present sequences which minimize the number of heteronuclear terms at the same time as recoupling the homonuclear interactions of the irradiated spins. The performance of the new sequences is tested on 13C labeled calcium formate. Experimental measurements of double-quantum 1H excitation indicate a relationship between good heteronuclear decoupling of the observed spin species and efficient recoupling of the irradiated spin species. The heteronuclear decoupling performance of the new sequences is significantly better than that obtained with an unmodulated radio-frequency field. The decoupling performance is improved further by breaking the pulse sequence symmetry in a controlled fashion. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479410
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  • 32
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    Electronic Resource
    Control of reaction rate by asymmetric two-state noise (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3349-3356 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We revisit the far from equilibrium escape problem across a fluctuating potential barrier that is driven by asymmetric, unbiased dichotomous noise. Our closed analytical solution for arbitrary noise strengths reveals new aspects of the so-called "resonant-activation" effect and leads to interesting implications regarding far from equilibrium or externally controlled chemical reaction processes. Specifically, a genuine asymmetry-induced variant of resonant activation within the constant intensity scaling scheme is discovered, and a new possibility to manipulate reaction rates and yields, as well as the balance between reactants and products, is put forward. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479619
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  • 33
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    Electronic Resource
    The accuracy of current density functionals for the calculation of electric field gradients: A comparison with ab initio methods for HCl and CuCl (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3357-3364 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The performance of current density functionals is analyzed in detail for the electric field gradients (EFG) of hydrogen chloride and copper chloride by comparison with ab initio methods and available experimental data. The range of density functionals applied shows good agreement with coupled cluster H and Cl field gradients for HCl, as has been demonstrated previously for other main-group element containing compounds. However, the performance of most density functionals is very poor for the Cu EFG in CuCl (EFG for Cu -0.44 a.u. at the coupled-cluster singles and doubles with perturbative triples [CCSD(T)] level, compared to, e.g., +0.54 a.u. at the B-LYP level). Only the "half-and-half" hybrid functionals give field gradients with the correct sign. The reason for the poor performance of the density functional theory is analyzed in detail comparing density functional with ab initio total electronic densities ρ(r). Due to the conservation of the number of particles, a change in the valence part of the electron density can lead to changes in the core part of the density. Errors in valence electronic properties like the dipole moment and in core properties like the Cu and Cl EFGs may therefore be connected. In fact the errors in both properties show a distinct linear relationship, indicating that if the dipole moment is correctly described by density functionals, the Cu and Cl EFGs may be accurate as well. Furthermore, at the atomic level, electric field gradients are described with reasonable accuracy by current density functionals as calculations for the Cu 2P excited state and the Cu2+ 2D ground state show. A comparison between the different density functionals shows that the incorrect behavior of the electronic density appears to be mainly due to defects in the exchange part of the functional.© 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479620
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  • 34
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    Electronic Resource
    On the frequency dependence of ultrasonically induced birefringence in isotropic phase of liquid crystal: 5CB (p-n-pentyl p′-cyanobiphenyl) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1580-1586 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical expressions for the ultrasonically induced birefringence of liquids are obtained in the frame work of de Gennes' phenomenological theory. The intensity and frequency dependence of ultrasonically induced birefringence in the isotropic phase of p-n-pentyl p′-cyanobiphenyl (5CB) was measured in order to examine the usefulness of birefringence measurements for investigating dynamical properties liquids. The observed birefringence was proportional to the square root of ultrasonic intensity. The birefringence divided by the square root of ultrasonic intensity increases with increasing frequency and appears to saturate when the ultrasonic frequency approaches the relaxation frequency of molecular reorientation. The observed values of birefringence were reproduced satisfactorily by the expression derived in this paper. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479417
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  • 35
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    Electronic Resource
    Stochastic bi-resonance without external signal in the CO+O2 catalytic oxidation reaction system (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1592-1594 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The noisy dynamic behavior of a surface catalytic reaction model to describe the oxidation of carbon monoxide is investigated when the control parameter is perturbed by external noise near a supercritical Hopf bifurcation point. Noise induced coherent oscillation (NICO) is observed and the NICO strength goes through two maxima with the increment of the noise intensity D from zero, characteristic of the occurrence of stochastic multiresonance without external signal. The frequency of the NICO also increases with the increment of D. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479419
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  • 36
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    Electronic Resource
    Pressure-induced structural and chemical changes of solid HBr (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1595-1607 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structural, dynamical, and electronic properties of solid HBr at high pressure are investigated using the ab initio constant pressure molecular dynamics method. A detailed analysis of the orientational distribution, and the reorientational and vibrational dynamics of the disordered phase I at ambient temperature showed that this phase can be described as a rotator phase with fluctuating hydrogen bonds up to pressures well over 10 GPa. We predict that the disorder at higher densities leads to cooperative proton-transfer dynamics. The approach to hydrogen-bond symmetrization is studied in phase I and the high pressure ordered phase III. The simulation results for phase III also indicate that this phase develops dielectric instabilities at high density. At pressures over 40 GPa we observe spontaneous formation of H2 with rearrangement of the Br lattice from fcc to hcp. The chemical reactivity is rationalized in terms of the electronic structure under conditions of near symmetrical hydrogen bonding. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479420
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  • 37
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    Electronic Resource
    The effect of attractions on the structure of fused sphere chains confined between surfaces (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1608-1614 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of attractive interactions on the behavior of polymers between surfaces is studied using Monte Carlo simulations. The molecules are modeled as fused sphere freely rotating chains with fixed bond lengths and bond angles; wall–fluid and fluid–fluid site–site interaction potentials are of the hard sphere plus Yukawa form. For athermal chains the density at the surface (relative to the bulk) is depleted at low densities and enhanced at high densities. The introduction of a fluid–fluid attraction causes a reduction of site density at the surface, and an introduction of a wall–fluid attraction causes an enhancement of site density at the surface, compared to when these interactions are absent. When the wall–fluid and fluid–fluid attractions are of comparable strength, however, the depletion mechanism due to the fluid–fluid attraction dominates. The center of mass profiles show the same trends as the site density profiles. Near the surface, the parallel and the perpendicular components of chain dimensions are different, which is explained in terms of a reorientation of chains. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479421
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  • 38
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    Electronic Resource
    Nonlinear dynamical properties of an oscillating tip–cantilever system in the tapping mode (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1615-1627 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamical properties of an oscillating tip–cantilever system are now widely used in the field of scanning force microscopy. The aim of the present work is to get analytical expressions describing the nonlinear dynamical properties of the oscillator in noncontact and intermittent contact situations in the tapping mode. Three situations are investigated: the pure attractive interaction, the pure repulsive interaction, and a mixing of the two. The analytical solutions obtained allow general trends to be extracted: the noncontact and the intermittent contact show a very discriminate variation of the phase. Therefore the measurement of the phase becomes a simple way to identify whether or not the tip touches the surface during the oscillating period. It is also found that the key parameter governing the structure of the dynamical properties is the product of the quality factor by a reduced stiffness. In the attractive regime, the reduced stiffness is the ratio of an attractive effective stiffness and the cantilever one. In the repulsive regime, the reduced stiffness is the ratio between the contact stiffness and the cantilever one. The quality factor plays an important role. For large values of the quality factor; it is predicted that a pure topography can be obtained whatever the value of the contact stiffness. For a smaller quality factor, the oscillator becomes more sensitive to change of the local mechanical properties. As a direct consequence, varying the quality factor, for example with a vacuum chamber, would be a very interesting way to investigate soft materials either to access topographic information or nanomechanical properties. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479422
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  • 39
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    Electronic Resource
    Inner shell excitation spectroscopy of transient molecules: HBS, HBO, and H3B3O3 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3468-3478 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Inner shell electron energy spectroscopy (ISEELS) was used to study HBS, HBO, and H3B3O3, reactive, transient species generated in situ. The reaction of H2S with crystalline boron in a quartz tube was used to produce thioborine (HBS) at ∼1100 °C, and borine (HBO) at ∼1200 °C. The reaction of H2O vapor with crystalline boron in a quartz tube at ∼1200 °C was used to produce boroxine (H3B3O3). These species were identified from their inner shell excitation spectra and mass spectrometry. The B 1s, S 2s, and S 2p ISEEL spectra of HBS, and the B 1s and O 1s spectra of HBO and H3B3O3 are reported and analyzed with the help of GSCF3 ab initio calculations. A reaction scheme is proposed for the generation of HBO from the reaction of H2S and boron in a heated quartz tube. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479632
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  • 40
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    Electronic Resource
    Molecular constants and Rydberg–Klein–Rees (RKR) potential curve for the Na2 1 3Σg− state (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3494-3497 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transitions into the doubly excited Na2 1 3Σg− state have been analyzed using near-dissociation expansions (NDE) to represent the vibrational energies and inertial rotational constants, while the centrifugal distortion constants were held fixed at "mechanically consistent" values calculated from the Rydberg–Klein–Rees (RKR) potential implied by those G(v) and Bv functions. The input data cover the range v=0 to 57 and N up to 47, and the fit yields vD=61.41(±0.10) and D0=3385.70(±0.2) cm−1. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479858
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    Four-dimensional quantum scattering calculations on the H+CH4→H2+CH3 reaction (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3508-3516 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-independent quantum scattering calculations have been performed to study the H+CH4→H2+CH3 reaction, using the analytic potential-energy surface developed by Jordan and Gilbert. A rotating bond umbrella (RBU) approximation with the implementation of a guided spectral transform subspace iteration technique has been applied together with a log-derivative method in hyperspherical coordinates. A single sector hyperspherical projection method was used to apply the boundary conditions to extract the S matrix at a large hyperradius. The results show that the H+CH4→H2+CH3 reaction occurs via a direct mechanism. The tunneling effect is pronounced, while there is little recrossing. Vibrational excitation of the C–H stretch and/or the H–CH3 bending modes of CH4 significantly enhance the reactivity. Exciting the umbrella mode of CH4 also enhance the reactivity, although less efficiently. The calculated thermal rate constants are larger than the experimental ones. However, good agreement has been obtained by including a barrier height correction of the potential function to make it agree with ab initio results. Finally, vibrational and rotational distributions of the reaction products are discussed in detail. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479634
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  • 42
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    Electronic Resource
    State-resolved collisional quenching of highly vibrationally excited pyridine by water: The role of strong electrostatic attraction in V→RT energy transfer (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3517-3525 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report experiments that investigate the influence of long-range attractive forces on collisional energy loss from highly vibrationally excited molecules. State-resolved studies of energy transfer from highly vibrationally excited pyridine (μ=2.2 D) to water (μ=1.8 D) in a low-pressure environment at 298 K have been performed using high-resolution transient absorption spectroscopy of water at λ(approximate)2.7 μm. Pyridine in its ground electronic state with 37 900 cm−1 of vibrational energy was prepared by absorption of pulsed ultraviolet light (λ=266 nm) to the S1 state, followed by rapid internal conversion to the S0 state. Collisions between vibrationally excited pyridine and water that result in rotational and translational excitation of the ground vibrationless state of H2O (000) were investigated by monitoring the populations of individual rotational states of H2O (000) at short times following pyridine excitation. The infrared probe of water was the highly allowed asymmetric stretching (000→001) transition. The nascent distribution of rotationally excited H2O (000) states is well described by a thermal distribution with a rotational temperature of Trot=770±80 K. Doppler-broadened transient linewidth measurements yield the velocity distributions of the recoiling H2O (000) molecules that correspond to center-of-mass translational temperatures of Ttrans∼515 K for all water rotational states investigated. Additionally, rate constants for energy gain in individual water states were determined, yielding an integrated rate constant of k2int=1.1×10−11 cm3 mol−1 s−1 for the appearance of H2O (000) with Erot=1000–2000 cm−1. These results are compared with previous relaxation studies of excited pyrazine (μ=0 D) with water and of excited pyridine with CO2 (μ=0 D), and the influence of electrostatic attraction on the relaxation dynamics is discussed. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479635
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    Electronic Resource
    Anharmonic phonon-polariton excitation through impulsive stimulated Raman scattering and detection through wave vector overtone spectroscopy: Theory and comparison to experiments on lithium tantalate (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3559-3571 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the generation of coherent, anharmonic phonon-polariton responses through impulsive stimulated Raman scattering with intense, crossed ultrafast excitation pulses. We find that the refractive index appears modulated at the stimulated scattering wave vector and the corresponding phonon-polariton frequency, and, due to anharmonicity, at stimulated scattering wave vector overtones and their corresponding frequencies. A realistic model of the soft lattice vibrational mode of the ferroelectric crystal lithium tantalate is considered in detail. Specific predictions for the magnitudes of different wave vector overtone contributions to the lattice displacement are made compared to experimental observations of anharmonic lattice responses. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479675
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  • 44
    Electronic Resource
    Electronic Resource
    Electron attachment to oxygen clusters studied with high energy resolution (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3548-3558 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Highly monochromatized electrons (with energy distributions of less than 30 meV FWHM) are used in a crossed beam experiments to investigate electron attachment to oxygen clusters (O2)n at electron energies from approximately zero eV up to several eV. At energies close to zero the attachment cross section for the reaction (O2)n+e→(O2)m− (for m=1, 2, and 3) rises strongly with decreasing electron energy compatible with s-wave electron capture to (O2)n. Peaks in the oxygen attachment cross sections present at higher energies ((approximate)80 meV, 193 meV, 302 meV) can be ascribed to vibrational levels of the anion populated by attachment of an electron to a single oxygen molecule within the target cluster via a direct Franck–Condon transition from the ground vibrational state v=0 to a vibrational excited state v′=7,8,9,... of the anion produced. The vibrational structures observed here for the first time can be quantitatively accounted for by model calculations using a microscopic model to examine the attachment of an electron to an oxygen molecule inside a cluster. This involves (i) molecular dynamics simulations to calculate the structure of neutral clusters prior to the attachment process and (ii) calculation of the solvation energy of an oxygen anion in the cluster from the electrostatic polarization of the molecules of the cluster. The occurrence of this polarization energy at the surface of larger clusters explains the appearance of an s-wave capturing cross section at 0 eV and the slightly smaller spacings (compared to the monomer case) between the peaks at finite energy, as observed experimentally. The relative transition probabilities from the ground state of the neutral oxygen molecule to the different vibrational levels of the anion are obtained by calculating the corresponding Franck–Condon factors thereby resulting in a reasonable theoretical fit to the observed yields of negatively charged oxygen molecules and clusters. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479637
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    Electronic Resource
    A computational study of homogeneous liquid–vapor nucleation in the Lennard-Jones fluid (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3581-3589 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Umbrella sampling Monte Carlo simulations are used to calculate free energy barriers to homogeneous liquid–vapor nucleation in the superheated Lennard-Jones fluid. The calculated free energy barriers decrease with increased superheating and vanish at the spinodal curve. A statistical geometric analysis reveals the existence of two types of voids: Small interstitial cavities, which are present even in the equilibrium liquid, and much larger cavities that develop as the system climbs the nucleation free energy barrier. The geometric analysis also shows that the average cavity size within the superheated liquid is a function of density but not of temperature. The critical nucleus for the liquid–vapor transition is found to be a large system-spanning cavity that grows as the free energy barrier is traversed. The weblike cavity is nonspherical at all superheatings studied here, suggesting a phenomenological picture quite different from that of classical nucleation theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479639
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  • 46
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    Electronic Resource
    Stark effect on the S1←S0 transition of cis-free base isobacteriochlorin in an n-octane single crystal at 5 K (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3612-3615 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution Stark effect measurements on the S1←S0(ππ*) origin of cis-free base isobacteriochlorin in single crystals of n-octane at 5 K are reported. The spectral splittings of the band at 15 822 cm−1 are linearly dependent on the applied electric field. The change in dipole moment (Δμ) was found to be 1.32 D and is parallel to the crystal's b-axis. This band blueshifted as the polarity of the solvents at room temperature was increased, which implies that Δμ is negative. To rationalize the large magnitudes and opposite signs of the cis and trans tautomers' Δμ values, we propose a simple valence-bond model based on ionic resonance structures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479640
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  • 47
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    Electronic Resource
    Relative mixing coefficients of zero-order 1B1(n,0,0) levels in the 1B1–1A2 hybrid wave functions of the vibronic bands of SO2 in the 32 184–34 040 cm−1 region (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1784-1785 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative mixing coefficients of the zero-order 1B1(n,0,0) vibrational levels present in the hybrid 1A2–1B1 wave functions are estimated according to the observed Franck–Condon patterns in dispersed fluorescence spectra. Non-Condon effects and spin–orbit coupling have been ignored in the treatment. The data cover nearly 50 cold vibronic bands in the 32 895–34 040 cm−1 region in addition to 9 vibronic bands in the 32 185–32 559 cm−1 region. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479441
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  • 48
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    Electronic Resource
    On the drift mobility of a molecular polaron in the presence of Coulomb traps (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3668-3674 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the drift mobility of a molecular polaron in the presence of an external applied field and Coulomb traps. The model is based on one previously developed for geminate recombination of photogenerated charge carriers. It is shown that the unusual combination of Poole–Frenkel-like field dependence and non-Arrhenius temperature dependence of the mobility, measured experimentally in molecular films, is well reproduced by this model. Our key result is that this nearly universal experimental behavior of the mobility arises from competition between rates of polaron trapping and release from a very low density of Coulomb traps. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479647
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  • 49
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    Electronic Resource
    Effect of subphase Ca++ ions on the viscoelastic properties of Langmuir monolayers (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3675-3678 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film's viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479648
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  • 50
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    Electronic Resource
    Fluorine atom abstraction by Si(100). I. Experimental (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3679-3695 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the interaction of low energy F2 with Si(100) at 250 K, a dissociative chemisorption mechanism called atom abstraction is identified in which only one of the F atoms is adsorbed while the other F atom is scattered into the gas phase. The dynamics of atom abstraction are characterized via time-of-flight measurements of the scattered F atoms. The F atoms are translationally hyperthermal but only carry a small fraction (∼3%) of the tremendous exothermicity of the reaction. The angular distribution of F atoms is unusually broad for the product of an exothermic reaction. These results suggest an "attractive" interaction potential between F2 and the Si dangling bond with a transition state that is not constrained geometrically. These results are in disagreement with the results of theoretical investigations implying that the available potential energy surfaces are inadequate to describe the dynamics of this gas–surface interaction. In addition to single atom abstraction, two atom adsorption, a mechanism analogous to classic dissociative chemisorption in which both F atoms are adsorbed onto the surface, is also observed. The absolute probability of the three scattering channels (single atom abstraction, two atom adsorption, and unreactive scattering) for an incident F2 are determined as a function of F2 exposure. The fluorine coverage is determined by integrating the reaction probabilities over F2 exposure, and the reaction probabilities are recast as a function of fluorine coverage. Two atom adsorption is the dominant channel [P2=0.83±0.03(95%, N=9)] in the limit of zero coverage and decays monotonically to zero. Single atom abstraction is the minor channel (P1=0.13±0.03) at low coverage but increases to a maximum (P1=0.35±0.08) at about 0.5 monolayer (ML) coverage before decaying to zero. The reaction ceases at 0.94±0.11(95%, N=9) ML. Thermal desorption and helium diffraction confirm that the dangling bonds are the abstraction and adsorption sites. No Si lattice bonds are broken, in contrast to speculation by other investigators that the reaction exothermicity causes lattice disorder. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479677
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    Valence-level photofragmentation of gaseous Si(CH3)Cl3 and solid-state analogs studied with synchrotron radiation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3714-3719 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociative photoionization channels of gaseous Si(CH3)Cl3 and ion desorption mechanisms of solid-state analogs following valence-level excitation have been investigated by means of photoionization mass spectroscopy, threshold photoelectron spectroscopy (TPES), and photon-stimulated ion desorption (PSID) using synchroton radiation. The adiabatic ionization threshold of the parent molecular ion was determined to be 11.18 eV, consistent with the value of 11.16 eV obtained from the TPES spectrum. An energy shift ∼0.8 eV toward lower binding energies for the orbitals of solid Si(CH3)Cl3 with respect to the gas phase values was observed. Two thresholds at 14.97 and 17.51 eV in the CH3+ photoionization efficiency spectrum are probably associated with the ionization of 2e″ and 11a1 orbitals, respectively. The H+ desorption threshold at 20.1 eV in the PSID spectrum may be attributed to the excitation of C 2s electron correlation states to the unoccupied states. The Cl+ desorption threshold at 19.9 eV is likely initiated by an Auger-stimulated desorption process.© 1999 American Institute of Physics. [S0021-9606(99)70731-2]
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    URL: http://dx.doi.org/10.1063/1.479651
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    Geometry of reorientational dynamics in supercooled poly(vinyl acetate) studied by 13C two-dimensional nuclear magnetic resonance echo experiments (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3720-3727 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A study of the reorientational segmental dynamics in supercooled poly(vinyl acetate) is presented, yielding detailed information about geometry and time scale of the motion close to the glass transition. The geometry information is derived from systematic variation of the evolution time in 13C 2D echo NMR measurements. The dynamics can be described as a superposition of angular jumps of approximately 10° and rotational diffusional processes. Both processes are related to the macroscopic α-relaxation. On the time scale of one jump process the orientation of a segment changes by about 2° via small step diffusion (〈0.6°). Furthermore the temperature dependence of this reorientatinal scenario is analyzed within the limits imposed by the experiment. All results are compared with previous 2H 2D NMR measurements on low-molecular glass formers. In both cases the loss of correlation, as described by conventional correlation times, results from a sequence of many distinct reorientational steps. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479652
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    Electronic Resource
    On the conformational structure of a stiff homopolymer (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3744-3752 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we complete the study of the phase diagram and conformational states of a stiff homopolymer. It is known that folding of a sufficiently stiff chain results in formation of a torus. We find that the phase diagram obtained from the Gaussian variational treatment actually contains not one, but several distinct toroidal states distinguished by the winding number. Such states are separated by first order transition curves terminating in critical points at low values of the stiffness. These findings are further supported by the off-lattice Monte Carlo simulation. Moreover, the simulation shows that the kinetics of folding of a stiff chain passes through various metastable states corresponding to hairpin conformations with abrupt U-turns. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479655
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  • 54
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    Host–guest interactions in fluorinated polymer electrolytes: A 7Li–13C NMR study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3761-3768 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gel-type electrolytes based on fluorinated polymers are of interest for electrochemical devices. We present a 7Li–13C solid-state NMR and modulated differential scanning calorimetry (MDSC) study of gel electrolytes based on a copolymer poly(vinylidene fluoride) (PVdF)–hexafluoropropylene (HFP) activated with a nonaqueous solution ethylene carbonate (EC)–propylene carbonate (PC)–LiN(CF3SO2)2. We show that the narrowing of the Li lineshape is decoupled from the glass transition. The behavior of the longitudinal relaxation times, T1, confirms that the host polymer matrix simply behaves like a quasiinert cage for the solution. These results are confirmed by 13C NMR at the magic angle (MAS) data, which show that the presence of the polymer does not significantly affect the chemical shift changes induced in the EC/PC carbons by the imide salt. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479656
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  • 55
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    Electronic Resource
    Structural, electronic, and bonding properties of liquid water from first principles (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3572-3580 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study, from first principles, structural, electronic, and bonding properties of liquid water. Our system is twice as large as that used in previous ab initio simulations and our computed structural properties are in good agreement with the most recent neutron scattering experiments. Moreover, the use of a novel technique, based on the generation of maximally localized Wannier functions, allowed us to describe the molecular charge distribution and the polarization effects in liquid water with a degree of accuracy not previously possible. We find that, in the liquid phase, the water molecule dipole moment has a broad distribution around an average value of about 3.0 D. This value is 60% higher than that of the gas phase and significantly larger than most previous estimates. A considerable increase is also observed in the magnitude of the average eigenvalues of the quadrupole moment tensor. We also find that the anisotropy of the electronic charge distribution of the water molecule is reduced in the liquid. The relevance of these results for current modeling of liquid water is discussed. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479638
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    Comment on "Reversible work of formation of an embryo of a new phase within a uniform macroscopic mother phase" [J. Chem. Phys. 108, 5498 (1998)] (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3769-3770 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We examine recently obtained expressions for the reversible work required to form a noncritical nucleus in a metastable vapor. We demonstrate that the expression obtained in by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)] is identical to that in by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)], thereby resolving the apparent contradiction between these two papers. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479667
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  • 57
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    Direct observation of nonadiabatic transitions in Na+rare-gas differential optical collisions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2853-2856 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the dynamics in optical collisions of Na with Ne, Ar, Kr, and Xe in a differential scattering experiment. We report the observation of nonadiabatic transitions in the excited collisional quasimolecule based on measurements of the population ratio of the Na(3p)2P1/2 and 2P3/2 fine-structure levels. Comparison with theoretical results shows a generally very good agreement over the range of collision energies (0.01–0.3 eV) scanned in our experiment, using the best available potentials. For the heavier rare-gas systems a strong influence of the BΣ–AΠ crossing on the population ratios is observed. We further extract a universal function for the nonadiabatic transition probability for these systems. In the thermal energy range, our results are in good qualitative agreement with data from gas phase optical collision experiments. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479566
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  • 58
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    Crossed beam reaction of the cyano radical, CN(X 2Σ+), with methylacetylene, CH3CCH (X 1A1): Observation of cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2857-2860 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical dynamics to form cyanopropyne, CH3CCCN (X 1A1), and cyanoallene, H2CCCHCN (X 1A′), via the neutral–neutral reaction of the cyano radical, CN (X 2Σ+), with methylacetylene, CH3CCH (X 1A1), is investigated under single collision conditions in a crossed molecular beam experiment at a collision energy of 24.7 kJ mol−1. The laboratory angular distribution and time-of-flight spectra of the C4H3N products are recorded at m/e=65, 64, 63, and 62. The reaction of d3-methylacetylene, CD3CCH (X 1A1), with CN radicals yields reactive scattering signal at m/e=68 and m/e=67 demonstrating that two distinct H(D) atom loss channels are open. Forward-convolution fitting of the laboratory data reveal that the reaction dynamics are indirect and governed by an initial attack of the CN radical to the π electron density of the β carbon atom of the methylacetylene molecule to form a long lived CH3CCHCN collision complex. The latter decomposes via two channels, i.e., H atom loss from the CH3 group to yield cyanoallene, and H atom loss from the acetylenic carbon atom to form cyanopropyne. The explicit identification of the CN vs H exchange channel and two distinct product isomers cyanoallene and cyanopropyne strongly suggests the title reaction as a potential route to form these isomers in dark molecular clouds, the outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479567
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  • 59
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    Frequency-dependent polarizabilities, hyperpolarizabilities, and excitation energies from time-dependent density-functional theory based on the quasienergy derivative method (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2878-2888 
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    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A time-dependent density-functional theory for systems in periodic external potentials in time is formulated on the assumption of the existence of the Floquet states from the quasienergy viewpoint. Coupling strength integration, which connects a noninteracting system with an interacting system, is introduced by using the time-dependent Hellmann–Feynman theorem. Coupled perturbed time-dependent Kohn–Sham equations are derived from the variational condition to the quasienergy functional with respect to parameters. Explicit expressions for frequency-dependent polarizability and first hyperpolarizability are given by the quasienergy derivative method. Excitation energies and transition moments are defined from poles and residues of frequency-dependent polarizabilities, respectively. In contrast to the previous theory, our formulation has the following three advantages: (1) The time-dependent exchange-correlation potential is defined by the functional derivative of the exchange-correlation quasienergy. (2) The formal expression for frequency-dependent polarizability, which corresponds to the exact sumover-states expression, can be obtained. (3) Explicit expressions for response properties which satisfy the 2n+1 rule can be automatically obtained. © 1999 American Institute of Physics.
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    URL: http://dx.doi.org/10.1063/1.479570
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  • 60
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    Electronic Resource
    Second- and third-order spin-orbit contributions to nuclear shielding tensors (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2900-2909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present analytical calculations of the electronic spin–orbit interaction contribution to nuclear magnetic shielding tensors using linear and quadratic response theory. The effects of the Fermi contact and the spin-dipole interactions with both the one- and two-electron spin–orbit Hamiltonians, included as first-order perturbations, are studied for the H2X (X=O, S, Se, and Te), HX (X=F, Cl, Br, and I), and CH3X (X=F, Cl, Br, and I) systems using nonrelativistic multiconfiguration self-consistent field reference states. We also present the first correlated study of the spin–orbit-induced contributions to shielding tensors arising from the magnetic field dependence of the spin–orbit Hamiltonian. While the terms usually considered are formally calculated using third-order perturbation theory, the magnetic-field dependent spin-orbit Hamiltonian requires a second-order calculation only. For the hydrogen chalcogenides, we show that contributions often neglected in studies of spin–orbit effects on nuclear shieldings, the spin-dipole coupling mechanism and the coupling of the two-electron spin–orbit Hamiltonian to the Fermi-contact operator, are important for the spin–orbit effect on the heavy-atom shielding, adding up to about half the value of the one-electron spin–orbit interaction with the Fermi-contact contribution. Whereas the second-order spin-orbit-induced shieldings of light ligands are small, the effect is larger for the heavy nuclei themselves and of opposite sign compared to the third-order contribution. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479572
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    Bond configurations in the Peierls–Hubbard model of small ring-shaped molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2392-2400 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Peierls–Hubbard model applied to N-membered ring-shaped molecules is investigated numerically and analytically. The bond configurations minimizing the total energy at half-filling of the electronic states are determined by a self-consistent method for N≤8 in a wide range of the electron–lattice and electron–electron coupling parameters. In the even-N case, only dimerized and homogeneous configurations have been found to be stable. Odd-N rings show three types of bond configurations depending on the coupling parameters. Two of these configurations have reflection symmetry whereas the third one is irregular.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479516
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  • 62
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    Vibrational-rotational energy transfer in H2-H2 collisions. I. Semiclassical decoupling approximation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2401-2406 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new semiclassical decoupling procedure for rotational projection states in rovibrationally inelastic atom-diatom and diatom-diatom collisions is developed. Computed vibrational self-relaxation rate constants for para-H2 and ortho-H2 are in good quantitative agreement (within a factor of 1.5, except for the lowest temperatures) with experimental data over the investigated temperature range 50–2000 K. This allows us to hope that also more detailed (nonmeasured) rate constants for rovibrational state-to-state transitions in molecular hydrogen, calculated by our new model, are sufficiently accurate for astrophysical applications. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479517
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    Ab initio calculation of the interaction potential for the krypton dimer: The use of bond function basis sets (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2407-2413 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Kr2 interaction potential is studied by ab initio calculations using several large basis sets containing high polarization functions and/or bond functions. It is shown that the addition of bond functions results in a dramatic improvement for the convergence of the calculated interaction energies. At the frozen-core MP4 level, the large atomic basis set such as [9s7p4d3f2g] recovered less than 75% of the experimental well depth. In contrast, the bond function basis set such as [9s7p4d3f]-{3s3p2d1f} produced a well depth of 617 μhartrees, over 99% of the experimental well depth. The frozen-core MP4 calculation appears to overestimate the well depth by about 25 μhartrees as compared to the calculation at the CCSD(T) level. On the other hand, the inclusion of core electron correlation at the MP4 level may contribute 13 μhartrees to the well depth. Beyond the potential minimum, the use of bond functions consistently gives significant improvement in the calculated potential from the highly repulsive wall to the attractive tail region. Final remarks are made about the counterpoise method and the use of bond functions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479518
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    Fluorescence quenching by reversible excimer formation: Kinetic study on the basis of generalized, non-Markovian rate equations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2414-2422 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetics of fluorescence quenching by reversible excimer formation has been studied theoretically on the basis of generalized, non-Markovian rate equations derived from a diffusion-kinetic hierarchy approach in the low-reactant density limit. It is demonstrated that, in contrast to the case of reversible excitation transfer [W. Naumann, J. Chem. Phys. 110, 3926 (1999)], compact rate kernel expressions can be derived not only for contact encounters but also for more realistic, longer-range reactivities. Given as functionals of so-called phenomenological excimer formation and dissociation coefficients, the rate kernel expressions allow a critical assessment of approximations based on time-scale separation arguments. An effective excimer formation coefficient is defined, which leads to simple and physically transparent formulas for the Laplace transforms of the excited monomer and excimer concentrations. The effect of the back reaction on the total fluorescence yield is discussed. The study also includes a critical comparison to analogous results obtained for the case of reversible energy transfer quenching. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479519
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    Quantum fluid dynamics in the Lagrangian representation and applications to photodissociation problems (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2423-2435 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper considers the practical utility of quantum fluid dynamics (QFD) whereby the time-dependent Schrödinger's equation is transformed to observing the dynamics of an equivalent "gas continuum." The density and velocity of this equivalent gas continuum are respectively the probability density and the gradient of the phase of the wave function. The numerical implementation of the QFD equations is carried out within the Lagrangian approach, which transforms the solution of Schrödinger's equation into following the trajectories of a set of mass points, i.e., subparticles, obtained by discretization of the continuum equations. The quantum dynamics of the subparticles which arise in the present formalism through numerical discretization are coupled by the density and the quantum potential. Numerical illustrations are performed for photodissociation of NOCl and NO2 treated as two-dimensional models. The dissociation cross sections σ(ω) are evaluated in the dramatically short CPU times of 33 s for NOCl and 40 s for NO2 on a Pentium-200 MHz PC machine. The computational efficiency comes from a combination of (a) the QFD representation dealing with the near monotonic amplitude and phase as dependent variables, (b) the Lagrangian description concentrating the computation effort at all times into regions of highest probability as an optimal adaptive grid, and (c) the use of an explicit time integrator whereby the computational effort grows only linearly with the number of discrete points. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479520
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    Vibrational spectroscopy of methanol and acetonitrile clusters in cold helium droplets (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2436-2443 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared molecular beam depletion spectroscopy of small methanol and acetonitrile clusters embedded in large helium clusters has been studied in the spectral region of the CO stretch and the CH3 rock mode from 1023 to 1059 cm−1. The results are compared with the experimental spectra of the corresponding free clusters generated in adiabatic expansions and calculations based on density functional theory or empirical potential models. For methanol clusters, the two types of experimental results are the same for the dimer and trimer structure. Different isomers are found in cold helium for the tetramer and pentamer, namely a monomer and dimer attached to a cyclic trimer. For acetonitrile clusters in helium, aside from the dimer, different structures are observed. The spectra from the trimer to the hexamer are dominated by structures which contain the antiparallel dimer as building block with D2d symmetry for the tetramer. They do not correspond to the minimum configurations observed for the free clusters. The fragmentation of the two cluster groups in helium droplets by electron impact ionization is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479521
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    Two-pulse laser control for selective photofragment orientation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3051-3057 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear wave packet dynamics in the potential well of a bound molecule can be controlled by an intense infrared (IR)-laser pulse. The phase of the nuclear wave packet motion is shown to depend on the phase of the laser field and the initial orientation of the molecule. We demonstrate, for diatomic heteronuclear molecules, that these spatial effects can be used to control the angular distribution of photofragments by selective dissociation of molecules with a given initial orientation from a sample of randomly oriented molecules. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479585
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    Two-dimensional nuclear magnetic resonance correlation spectroscopy at zero field (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3077-3082 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three methods for two-dimensional correlation nuclear magnetic resonance spectroscopy at zero field are discussed. All three involve coherence transfer via longitudinal polarization, double quantum coherence, or both in parallel. The double quantum pulse sequences exploit the spinor property of spin states. These sequences have been applied to connected Δm=1 transitions, as well as for the indirect detection of forbidden or nearly forbidden Δm〉1 transitions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479588
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    Interaction-site-model description of collective excitations in liquid water. I: Theoretical study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3083-3094 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Collective excitations in liquid water are investigated using the recently developed theory for dynamics of molecular liquids which is based on the interaction-site model for polyatomic fluids, the projection-operator formalism of Zwanzig and Mori, and the simple approximation scheme for memory functions. It is shown that all the essential features of collective excitations in water, reported previously by neutron-scattering experiments, molecular dynamics simulations and dielectric theories, are well reproduced by the present theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479589
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  • 70
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    On the strongly bound B 3Π state of the CAr van der Waals complex: Bonding and predissociation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3070-3076 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the open shell van der Waals molecule, CAr, the potential energy curves (PECs) for the B 3Π and 1 5Σ− states, the B 3Π–1 5Σ− spin–orbit coupling and the B 3Π fine structure splitting are determined using multireference configuration interaction wave functions as large as ∼8 million configuration state functions. The B 3Π state is strongly bound, with De=5100 cm−1. Re(B 3Π)=3.7a0 and is considerably shorter than Re(X 3Σ−)=6.07 a0. The PEC for the repulsive 1 5Σ− state crosses that of the B 3Π state at Rx(1 5Σ−,B 3Π)=3.31a0 leading to spin–orbit induced predissociation. The B 3Π–1 5Σ− spin–orbit coupling is the result of valence-Ryberg mixing in the B 3Π state and is considerably enhanced by the heavy atom effect. The heavy atom effect is also reflected in a marked decrease in the fine structure splitting of the B 3Π state with increasing vibrational level. The implications of these results for using CAr(B 3Π) in laser induced fluorescence detection of CAr(X 3Σ−,v) are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479587
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    Rotational-resolved pulsed field ionization photoelectron study of NO+(X 1Σ+,v+=0–32) in the energy range of 9.24–16.80 eV (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3058-3069 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have obtained rotationally resolved pulsed filed ionization photoelectron (PFI-PE) spectra of NO in the energy range of 9.2–16.8 eV, covering ionization transitions of NO+(X 1Σ+,v+=0–32,J+)←NO(X 2Π3/2,1/2,v″=0,J″). The PFI-PE bands for NO+(X 1Σ+,v+=6–32) obtained here represent the first rotationally resolved spectroscopic data for these states. The simulation using the Buckingham–Orr–Sichel model provides accurate molecular constants for NO+(X 1Σ+,v+=0–32), including ionization energies, vibrational constants (ωe+=2 382.997±0.122 cm−1, ωe+χe+=17.437 84±0.000 90 cm−1, ωe+ye+=0.063 209 5±3.2×10−6 cm−1, and ωe+ze+=−0.001 400 0±7.2×10−8 cm−1), and rotational constants (Be+=1.996 608±0.006 259 cm−1, αe+=0.020 103±6.3×10−5 cm−1, and γe+=−(7.22±2.26)×10−6 cm−1). For v+=0–15, the rotational branches are ΔJ=J+−J″=±1/2, ±3/2, ±5/2, ±7/2, and ±9/2, which correspond to the formation of photoelectron angular momentum states l=0, 1, 2, and 3. The ΔJ=±1/2, ±3/2, ±5/2, ±7/2, ±9/2, and ±11/2 rotational branches are observed in the spectra for v+=16–32, revealing the production of continuum photoelectron states l=0, 1, 2, 3, and 4. The maximum ΔJ value and intensities for high ΔJ rotational branches are found to generally increase as v+ is increased in the range of 0–32. This observation is attributed to an increase in inelastic cross sections for collisions between the outgoing photoelectron and the nonspherical molecular ion core as the bond distance for NO+ is increased. Thus, this observation can be taken as strong support for the electron-molecular-ion-core scattering model for angular momentum and energy exchanges in the threshold photoionization of NO. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479586
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    Fifth-order two-dimensional Raman spectra of CS2 are dominated by third-order cascades (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3105-3114 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have demonstrated that fifth-order stimulated Raman spectra of the intermolecular modes in CS2 are dominated by cascading third-order processes. Previous studies have successfully discriminated against a sequential cascading process, but did not account for parallel third-order cascades. All of our measured spectra were successfully simulated considering only cascades built directly from our measured third-order spectra. Using an appropriately chosen phase matching geometry we also measured the sequential cascade, which should exist with equal probability to the parallel cascade. When employing a phase matching geometry that provided substantial discrimination against all of the third-order cascades we were not able to measure any signal. We assign an upper limit for the true fifth-order signal of 2% of the cascaded signal. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479591
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    Effects of excited state mixing on transient absorption spectra in dimers: Application to photosynthetic light-harvesting complex II (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3121-3132 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The excited state mixing effect is taken into account considering the difference spectra of dimers. Both the degenerate (homo) dimer as well as the nondegenerate (hetero) dimer are considered. Due to the higher excited state mixing with the two-exciton states in the homodimer, the excited state absorption (or the difference spectrum) can be strongly affected in comparison with the results obtained in the Heitler–London approximation. The difference spectrum of the heterodimer is influenced by two resonance effects (i) mixing of the ground state optical transitions of both monomers in the dimer and (ii) mixing of the excited state absorption of the excited monomer with the ground state optical transition in the nonexcited monomer. These effects have been tested by simulating the difference absorption spectra of the light-harvesting complex of photosystem II (LHC II) experimentally obtained with the 60 fs excitation pulses at zero delay times and various excitation wavelengths. The pairs of coupled chlorophylls a and b for simulations have been taken from the best LHC II assignment model obtained by simulating the steady-state spectra and the transient absorption at various excitation wavelengths. Qualitatively the spectral peculiarities of the difference spectra are explained by means of the resonance interpigment interactions, which are responsible for the excited state mixing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479593
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    Differential cross sections for H+D2→HD (v′=2, J′=0,3,5)+D at 1.55 eV (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2490-2498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoloc technique with core extraction of the nascent product laboratory speed distribution in a Wiley–McLaren time-of-flight spectrometer has been used to measure differential cross sections for the reaction H+D2→HD (v′=2, J′=0,3,5)+D at collision energies ∼1.55 eV. We find that the peak of each angular distribution shifts from complete backward scattering toward side scattering as the rotational excitation of the product increases. We found the same trend in our previous study of H+D2→HD (v′=1, J′=1,5,8)+D at ∼1.70 eV. We conclude that the same type of correlation exists between impact parameter and rotational quantum number in both product vibrational manifolds. Further analysis of the HD (v′=2, J′) differential cross section data reveals, however, a clear tendency of this vibrational manifold to scatter sideways at lower J′ than HD(v′=1, J′). Within the framework of a line-of-centers model with nearly elastic specular scattering, this result implies that smaller impact parameters lead to more vibrationally excited products. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479527
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    Time-dependent density functional calculations on the electronic absorption spectrum of free base porphin (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2499-2506 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three high-level correlated ab initio studies have recently been performed on the electronic absorption spectrum of free base porphin (FBP), but significant differences between the various assignments of the low-lying bands remain. In view of the importance of FBP as the basic building block of the porphyrins, further reliable results are evidently required and are provided here, using time-dependent density functional theory (TDDFT). Our results strongly support the recent CASPT2 interpretation which is consistent with the traditional interpretation, stating that the intense B band (or Soret band) is due to the two close-lying excitations 2 1B2u and 2 1B3u. As in the CASPT2 paper, we attribute all low-lying bands to pairs of 1B2u–1B3u excitations. The interpretation of the combined B–N band system is discussed in some detail. The effects of basis set, geometry, and choice of exchange-correlation potential are considered as well. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479617
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    Reaction of state-selected ammonia ions with methane (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2507-2512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have investigated the reaction of ammonia ions with methane molecules (CD4) over the collision energy range of 0.5–10.0 eV and for ammonia ion vibrational states ranging from ν2=1–10. Under these conditions, the two main product channels are NH3D+ and CD3+. The cross section for formation of NH3D+ is enhanced with increasing internal energy at collision energies below 6.0 eV, and independent of internal energy at higher collision energies. The enhancement is greater for forward-scattered products indicating that ammonia-ion vibrational energy enhances reactivity at large impact parameters. The mechanism for formation of CD3+ involves collision-induced dissociation of CD4 (or NH3+) which leads to the formation of a short-lived [NH3CD3]+ ([NH2CD4]+) complex, which then decays to products. This reaction is found not to be vibrationally mode selective, which is consistent with the hypothesis that mode selectivity in reactions of ammonia ions is driven by the Franck–Condon overlap whenever charge transfer is involved. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479528
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    Observation of linear isomers of the ionized rare gas tetramers Ar4+ and Xe4+ (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2513-2518 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ionized rare gas clusters Ar4+ and Xe4+ have been studied by photofragmentation. Center-of-mass velocities of the neutral and ionized photofragments have been measured for photon energies between 1.6 and 4.4 eV. In almost all of the examined photon energy region, both clusters exhibit fragment velocity distributions which show that they consist of a linear ionized trimer with an additional atom loosely attached to its side. For the lowest photon energies, however, fragmentation patterns are observed which can only be explained by a linear tetramer structure. This demonstrates that stable linear isomers of the ionized rare gas tetramers exist. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479529
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    Grand canonical ensemble Monte Carlo simulation of a lipid bilayer using extension biased rotations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10770-10773 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The cavity-biased grand-canonical ensemble method was applied to the simulation of a lipid bilayer using an enhanced Monte Carlo sampling technique. The enhancements include controlling the torsion and molecular rotation step size based on the lipid's conformation and controlling the order of torsion change attempts. It was found that the proposed sampling technique significantly enhances the rate of sampling of the lipid conformations while the grand-canonical ensemble implementation ensures that the water can both penetrate and escape pockets in the bilayer. The latter will be particularly important for simulating bilayers with embedded molecules. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480442
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    Combining coupled cluster and perturbation theory (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10815-10826 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single reference coupled cluster (CC) singles and doubles theory is combined with low-order perturbation theory (PT) to treat ground state electron correlation. Two variants of the general scheme are discussed that differ in the type of amplitudes that are approximated perturbatively and which are treated to infinite order. The combined CC/PT methods to include ground state correlation are merged with equation-of-motion (EOM) and similarity transformed EOM methods to describe excitation spectra of the highly correlated s-tetrazine, MnO4− and Ni(CO)4 systems. It is shown that the computationally efficient CC/PT schemes can reproduce full CCSD results even if perturbation theory by itself is a very poor approximation, as is the case for many transition metal compounds. In a second test CC/PT is applied to determine ground state equilibrium molecular structures and harmonic vibrational frequencies for a set of small molecules. Using either variant of CC/PT, full CCSD geometries are easily recovered, while vibrational frequencies can be more sensitive to details of the approximation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480445
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  • 80
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    A simple semiclassical approach to the Kramers' problem (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10852-10858 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that the Wigner–Leggett–Caldeira equation for Wigner phase space distribution function which describes the quantum Brownian motion of a particle in a force field in a high temperature, ohmic environment can be identified as a semiclassical version of Kramers' equation. Based on an expansion in powers of (h-dash-bar), we solve this equation to calculate the semiclassical correction to Kramers' rate. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480449
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  • 81
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    Semiclassical dynamics of nonadiabatic transitions in discrete-state systems using spin coherent-state path integrals (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10843-10851 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a semiclassical method for simulating the dynamics of nonadiabatic transitions in a discrete-state quantum system coupled to a bath of explicit continuous coordinates. This method employs a coherent-state formulation of the path integrals for the discrete system whose dynamics is described by spin operators. This spin coherent-state formulation allows the discrete system to be mapped onto a continuous coordinate. Stationary approximations of the resulting coherent-state path integrals of the system plus bath lead to quasiclassical equations of motion which can be solved numerically by direct integration. This algorithm reduces the problem to a number of simple classical trajectory calculations and does not require calculating any fluctuation determinants. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480448
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  • 82
    Electronic Resource
    Electronic Resource
    Spin polarization of zero kinetic energy electrons from HBr (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10883-10886 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The range of observables in zero kinetic energy (ZEKE) electron spectroscopy of molecules, previously restricted to the total electron intensity, was extended by measuring the integral spin polarization of ZEKE electrons at the HBr Ω+=3/2 thresholds after single-photon excitation with narrow-band circularly polarized light. A comparison with calculated values from multichannel quantum defect theory underlines the importance of autoionization for the decay dynamics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480405
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  • 83
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    Electronic Resource
    Quantum Monte Carlo simulation of intermolecular excited vibrational states in the cage water hexamer (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10866-10875 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rigid-body diffusion Monte Carlo simulations of the ground state and ten low-lying intermolecular excited vibrational states for the cage form of (H2O)6 are reported. The excited states are found by a nodal optimization procedure in which the fundamental excited-state nodes are constructed from the harmonic normal coordinates. The anharmonic effects in the excited states are found to be large. One of the states with relatively large transition intensity involves primarily flipping motions of the free OH bonds on the doubly bound monomers, and is assigned to the vibration–rotation–tunnelling band observed experimentally by Liu et al. [Nature 301, 501–503 (1996)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480451
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  • 84
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    Electronic Resource
    One- and two-body densities for the beryllium isoelectronic series (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10903-10909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One- and two-body densities in position space have been calculated for the atomic beryllium isoelectronic series starting from explicitly correlated multideterminant wave functions. The effects of electronic correlations have been systematically studied by comparing the correlated results with the corresponding Hartree–Fock ones. Some expectation values such as 〈δ(r)〉, 〈rn〉, 〈δ(r12)〉, 〈r12n〉, 〈δ(R)〉, and 〈Rn〉, where r, r12, and R stand for the electron–nucleus, interelectronic, and two electron center of mass coordinates, respectively, have been obtained. All the calculations have been carried out by using the Monte Carlo algorithm. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480485
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  • 85
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    Electronic Resource
    Lithium perchlorate ion pairing in a model of amorphous polyethylene oxide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3302-3308 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a molecular dynamics study of pairing and dynamics of lithium cation and perchlorate anion in a previously reported model of amorphous polyethylene oxide. We are particularly interested in the question of whether these ions pair in the model, as previously reported experimentally. We calculate the potential of mean force between a lithium and perchlorate ion in the system for several temperatures when a pair of ions is at various separation distances in our model. We find evidence for two minima in the potential of mean force, one at lithium–chlorine separations of 3.5 Å and about 6.5 Å. We studied the same system with five ion pairs in the system and again find two minima at the same separation distances but in this case there is evidence of entropic effects in the binding free energy of the pairs at 3.5 Å. A study of radial distribution functions permits us to deduce information concerning the structure of the paired states. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479609
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  • 86
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    Electronic Resource
    A new six-dimensional analytical potential up to chemically significant energies for the electronic ground state of hydrogen peroxide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2565-2587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations of the electronic ground state potential energy surface (PES) of hydrogen peroxide covering, in an almost global fashion, all six internal degrees of freedom by two different ab initio techniques. Density functional theory (DFT) calculations using the Becke 3 parameter Lee–Yang–Parr (B3LYP) hybrid functional and multiconfigurational second order perturbation theory (CASPT2) calculations, both using large basis sets, are performed for a wide range of geometries (8145 DFT and 5310 CASPT2 single-point energies). We use a combined data set of mostly DFT with additional CASPT2 ab initio points and the complete CASPT2 surface to fit a total of four different 6D analytical representations. The resulting potentials contain 70–76 freely adjusted parameters and represent the ground state PES up to 40000 cm−1 above the equilibrium energy with a standard deviation of 100–107 cm−1 without any important artifacts. One of the model surfaces is further empirically refined to match the bond dissociation energy D0 for HOOH→2OH. The potentials are designed for energy regions accessible by vibrational fundamental and overtone spectroscopy including the dissociation channel into hydroxyl radicals. Characteristic properties of the model surfaces are investigated by means of stationary point analyses, torsional barrier heights, harmonic frequencies, low-dimensional cuts and minimum energy paths for dissociation. Overall good agreement with high-level ab initio calculations, especially for the CASPT2 based potentials, is achieved. The drastic change in geometry at intermediate O–O distances, which reflects the transition from covalent to hydrogen bonding, is reproduced quantitatively. We calculate fully 6D anharmonic zero point energies and ground state torsional splittings with the diffusion quantum Monte Carlo method in perfect agreement, within statistical error bars, with experiment for the CASPT2 based potentials. Variational vibrational calculations in the (4+2)D adiabatic approximation yield energy levels and torsional splittings from the ground state up to predissociative states, satisfactorily reproducing the experimental transition wavenumbers. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479534
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  • 87
    Electronic Resource
    Electronic Resource
    Electronic nonadiabaticity in highly vibrationally excited O2(X 3Σg−): Spin-orbit coupling between X 3Σg− and b 1Σg+ (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2588-2594 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report full quantum-state-resolved spectra of highly vibrationally excited O2(X 3Σg−,v=26–31). In addition to providing high precision molecular constants for several new vibrational levels, we observe a local spectral perturbation of X 3Σg−(v=28). We present a deperturbation analysis of the observed spectra and assign the perturber to b 1Σg+(v=19). We predict a crossing between the b 1Σg+ and X 3Σg− state at an internuclear separation R=2.45±0.1 Å, somewhat further extended and higher in energy than the outer classical turning point of O2(X 3Σg−,v=28). Using the appropriate vibrational overlap integral, we are able to determine the spin–orbit interaction between these two electronic states, which is 200±20 cm−1 in the vicinity of the crossing. These results suggest that the collision dynamics of highly vibrationally excited O2(X 3Σg−) may involve excited potential surfaces. Furthermore, they imply that present theoretical approaches to the O4 problem, which use a single potential surface, may not be adequate. Possible implications regarding nonequilibrium models of stratospheric ozone formation and the dynamics of the O+O3→2O2 reaction are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479618
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  • 88
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    Electronic Resource
    Photodissociation of HBr molecules and clusters: Anisotropy parameters, branching ratios, and kinetic energy distributions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2595-2605 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultraviolet photolysis of HBr molecules and (HBr)n clusters with average size around n¯=9 is studied at three different wavelengths of 243, 205, and 193 nm. Applying polarized laser light, the kinetic energy distribution of the hydrogen photofragment is measured with a time-of-flight mass spectrometer with low extraction fields. In the case of HBr monomers and at 243.1 nm, an almost pure perpendicular character (β=−0.96±0.05) of the transitions is observed leading to the spin–orbit state Br(2P3/2). The dissociation channel associated with the excited state Br*(2P1/2) is populated by a parallel transition (β*=1.96±0.05) with a branching ratio of R=0.20±0.03. At the wavelength of 193 nm, about the same value of R=0.18±0.03 is found, but both channels show a mainly perpendicular character with β=−0.90±0.10 for Br and β*=0.00±0.10 for Br*. The results for 205 nm are in between these two cases. For the clusters at 243 nm, essentially three different groups appear which can be classified according to their kinetic energy: (i) A fast one with a very similar behavior as the monomers, (ii) a faster one which is caused by vibrationally and rotationally excited HBr molecules within the cluster, and (iii) a slower one with a shoulder close to the fast peak which gradually decreases and ends with a peak at zero velocity. The zero energy fragments are attributed to completely caged H atoms. The angular dependence of the group (iii) is isotropic, while that of the other two is anisotropic similar to the monomers. At 193 nm only the fast and the slow part is observed without the peak at zero energy. Apparently the kinetic energy is too large to be completely dissipated in the cluster. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479535
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  • 89
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    Electronic Resource
    Photodissociation of Ar–HCl: An energy-resolved study of the dynamics of total fragmentation into H+Ar+Cl (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2606-2619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: UV photolysis of Ar–HCl is simulated by means of an exact wave packet treatment in three dimensions. The focus of the work is on the mechanism of indirect dissociation of the hydrogen atom, which leads to total fragmentation of Ar–HCl into H, Ar, and Cl. The results predict for this photodissociation path a probability of about 13% of the photolysis process. The remaining probability would be associated with direct photodissociation of the H fragment. Kinetic-energy distributions of the hydrogen fragments produced by indirect photodissociation are calculated for different excitation energies of Ar–HCl. The distributions reflect a pronounced structure of peaks associated with broad and overlapping resonances of the system. The resonance structure is present in the whole energy range covered by the absorption spectrum. Hydrogen atoms initially populating the resonances can dissociate from the cluster extensively cooled down, after several collisions with Ar and Cl. A mechanism is suggested for the fragmentation process due to indirect photodissociation, which involves successive jumps of the hydrogen to lower-energy resonances, induced by the collisions. A classical collisional model is proposed to rationalize qualitatively the fragmentation dynamics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479536
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  • 90
    Electronic Resource
    Electronic Resource
    Screening ionic motion in sodalite cages: A dynamical study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2761-2769 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamical evolution of protonated helium clusters inside sodalite cages (silica-sodalite and acidic sodalite) is followed via a Car–Parrinello approach. The static simulations give framework structural and electronic features that agree with previous experimental and theoretical data. The protonated helium clusters are used to screen the positive charge borne by a "naked" proton, and are intended as simplified models of the solvation sphere of H+. The action of the framework on the solvation shell of the proton is shown to be mainly due to induction-polarization or Coulombic forces, with a minor contribution of resonant energy exchange between the framework modes and the cluster oscillators. The covalent nature of the zeolitic O–H bond is determined with the aid of the bond order conservation principle. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479553
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  • 91
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    A comparison of hydrogen-bonded and van der Waals isomers of phenol⋅⋅nitrogen and phenol⋅⋅carbon monoxide: An ab initio study (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1955-1963 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hydrogen-bonded and van der Waals isomers of phenol⋅⋅nitrogen and phenol⋅⋅carbon monoxide in their neutral electronic (S0) and cation ground state (D0) were studied using ab initio HF/6-31G*, MP2/6-31G*, and B3LYP/6-31G* methods. The hydrogen-bonded isomers have the ligand bound via the hydroxyl group of the phenol ring, while the van der Waals isomers studied have the ligand located above the aromatic ring. For both complexes, the hydrogen-bonded isomer was found to be the most stable form for both the S0 and the D0 states. For phenol⋅⋅carbon monoxide, twice as many isomers as compared to phenol⋅⋅nitrogen were found. The hydrogen-bonded isomer with the carbon end bonded to the hydroxyl group was the most stable structure for both the S0 and the D0 states. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479508
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  • 92
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    Mass analyzed threshold ionization of phenol⋅CO: Intermolecular binding energies of a hydrogen-bonded complex (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1947-1954 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: [Phenol⋅CO]+ was studied using a combination of two-color resonant zero kinetic energy (ZEKE) spectroscopy and mass analyzed threshold ionization (MATI) spectroscopy to investigate the interaction of the CO ligand with a hydrogen-bonding cation. Vibrational progressions were observed in three intermolecular modes, the in-plane bend (42 cm−1), stretch (130 cm−1), and in-plane wag (160 cm−1), and are consistent with a planar hydrogen-bonded structure where the CO bonds through the carbon atom to the phenol OH group. Dissociation energies for the S0, S1, and D0 states were determined as 659±20, 849±20, and 2425±10 cm−1, respectively. The cationic and neutral dissociation energies of the phenol⋅CO complex are considerably stronger than those of phenol⋅N2, demonstrating the extent to which the larger quadrupole of CO affects the strength of binding. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479463
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  • 93
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    Electronic Resource
    Theoretical determination of the absolute electron impact ionization cross-section function for silver clusters Agn (n=2–7) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1964-1971 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recently developed semiclassical approach (DM formalism) was used to calculate the absolute total electron-impact single ionization cross sections for silver clusters Agn (n=2–7) from threshold to 1000 eV. Similar to other cluster properties, a clear odd–even effect has been observed for the calculated cross sections and is ascribed to the effective electron numbers in the valence shell. The only available experimental data for comparison are partial cross sections for the production of the singly charged parent ions for the monomer up to the tetramer. No experimental data are available as yet for any larger clusters nor for the total ionization cross sections. Nevertheless, a comparison of the results of the present calculations with calculations using additivity rules applied to molecules and clusters gives valuable insight into the ionization behavior of clusters as a function of cluster size and thus elucidates the transition from a molecular-type situation where the cross sections of the constituents are additive to a cluster-type situation where geometric effects lead to a n2/3-dependence in the limit of large cluster sizes n. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479464
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  • 94
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    Quantum mechanical study of the vibrational relaxation of O2+ colliding with Kr (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1972-1978 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coupled states calculations on the vibrational relaxation of O2+(v=1) colliding with Kr are reported. In the first stage, calculations have been done on single potential energy surfaces and different surfaces have been used. Then treating O2+ as a molecule in a Π ground electronic state, we have performed quantum scattering calculations on the vibrational relaxation on two 1 2A″ and 1 2A′ surfaces. A significant effect due to the inclusion of the second potential surface is reported. A comparison of the calculated rate constants with available experimental data is made. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479465
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  • 95
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    Electronic Resource
    Vibrational spectrum of B2C in argon at 10 K (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1988-1992 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational spectrum of B2C has been observed for the first time in solid argon by Fourier-transform infrared spectroscopy. Absorption frequencies of the three boron isotopomers of cyclic symmetric B2C, previously deduced by ab initio theory, are in accord with measured frequencies, which enables assignment of an absorption at 1392.8 cm−1 to the ν1(a1) fundamental of B2C(1A1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479467
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  • 96
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    Electronic Resource
    Quadratic response of molecules in a nonequilibrium and equilibrium solvation model: Generalizations to include both singlet and triplet perturbations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2678-2685 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quadratic response theory for equilibrium and nonequilibrium solvation has been extended to include both singlet and triplet perturbations. The approach is tested by investigating the effect of solvent on the phosphorescence lifetime of formaldehyde. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479543
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  • 97
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    Exponential intermolecular dynamics in optical Kerr effect spectroscopy of small-molecule liquids (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2686-2694 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optical Kerr effect spectroscopy has been employed to study the behavior of six symmetric-top liquids (acetonitrile, acetonitrile-d3, benzene, carbon disulfide, chloroform, and methyl iodide) over a broad range of temperatures. In all of the liquids, an exponential intermolecular response is observed on a time scale of a few hundreds of femtoseconds. Comparison of the temperature dependence of the time scale of this relaxation with the viscosity and single-molecule and collective orientational times in the liquids suggests that the exponential relaxation arises from motional narrowing. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479544
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  • 98
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    Fractional power dependence of mean lifetime of electron transfer reaction on viscosity of solvent (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2665-2677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dynamical effects of a solvent (environment) on an electron transfer (ET) reaction are investigated by using the Sumi–Marcus reaction–diffusion equation; this equation describes the time evolution of population distribution function of a reactant in a slow nuclear coordinate system. Assuming that viscosity of the solvent (environment) is proportional to a relaxation time scale of the slow nuclear mode, power dependence of a mean lifetime of ET on the relaxation time scale becomes the same as the one on the viscosity. Therefore, the former power dependence is investigated instead of the latter, and it is found that the power in the limit of the (infinitely) large relaxation time scale is 1−r when r〈1, and 0 when 1≤r, where r is the ratio of the reorganization energy of fast nuclear modes to the slow nuclear mode. However, this limit cannot always be reached in a realistic situation. Therefore, the present theory is extended to a large but finite relaxation time scale. The values of the power obtained by the present theory are in reasonable agreement with the ones calculated numerically by W. Nadler and R. A. Marcus [J. Chem. Phys. 86, 3906 (1987)]. Finally, a difficulty in numerical calculations is shown. An expansion of the population distribution function in some basis set of functions is common in numerical calculations. However, the use of that finite basis set of functions which is independent of the relaxation time scale leads to a value of the power that is either zero or unity in the limit of the large relaxation time scale, and as such cannot reproduce the correct asymptotic behavior of the mean lifetime. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479542
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  • 99
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    Dynamical properties of the soft sticky dipole model of water: Molecular dynamics simulations (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2701-2709 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dynamical properties of the soft sticky dipole (SSD) model of water are calculated by means of molecular dynamics simulations. Since this is not a simple point model, the forces and torques arising from the SSD potential are derived here. Simulations are carried out in the microcanonical ensemble employing the Ewald method for the electrostatic interactions. Various time correlation functions and dynamical quantities associated with the translational and rotational motion of water molecules are evaluated and compared with those of two other commonly used models of liquid water, namely the transferable intermolecular potential-three points (TIP3P) and simple point charge/extended (SPC/E) models, and also with experiments. The dynamical properties of the SSD water model are found to be in good agreement with the experimental results and appear to be better than the TIP3P and SPC/E models in most cases, as has been previously shown for its thermodynamic, structural, and dielectric properties. Also, molecular dynamics simulations of the SSD model are found to run much faster than TIP3P, SPC/E, and other multisite models. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479546
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  • 100
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    Scattered and recoiled ion fractions from LiTaO3(100) surfaces with different electrical properties (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2720-2725 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-of-flight scattering and recoiling spectrometry (TOF-SARS) was used to investigate the scattered and recoiled ion fractions from 3 keV Ar+ ion beams on LiTaO3(100) single crystals. The TOF-SARS measurements were found to be sensitive to the electrical properties of the crystal. ac impedance measurements of the electrical conductivity showed that LiTaO3 is an insulator at room temperature and that its conductivity increases by ∼103 at temperatures in the range 100–200 °C. This increase in conductivity could be monitored in TOF-SARS by measuring the current through the crystal induced by the impinging Ar+ ions as a function of temperature. The activation energy for this transition was estimated from both the impedance and scattering measurements to be ∼1 eV. Azimuthal anisotropy of the scattered Ar+ ions from Ta atoms was observed at room temperature but not at elevated temperatures. Scattered Ar+ ion fraction measurements showed that scattered Ar+ ions are enhanced by charge buildup on the LiTaO3 surface, whereas recoiled ions are not affected. The effects of surface charging phenomena on TOF-SARS could be eliminated by either heating the LiTaO3 crystal to ∼200 °C or by application of a low energy electron beam to the crystal surface. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479548
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