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  • 1
    Electronic Resource
    Electronic Resource
    The C4H8.bul.+ potential energy surface. 1. The cyclobutane radical cation (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 5776-5782 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00066a050
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  • 2
    Electronic Resource
    Electronic Resource
    The C4H8.bul.+ potential energy surface. 2. The (C2H4)2.bul.+ complex cation and its reaction to the radical cations of cyclobutane and 1-butene (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 5783-5789 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00066a051
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  • 3
    Electronic Resource
    Electronic Resource
    Small doped 3He clusters: A systematic quantum chemistry approach to fermionic nuclear wave functions and energies (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 10214-10219 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A novel approach for calculating nuclear wave functions and energies of 3He clusters doped with an atomic or molecular impurity is developed. It adopts the systematic and well developed methodology of quantum chemistry employing an analogy between electrons bound by Coulomb forces to the nuclei and fermionic 3He atoms clustered around a dopant species. The differences primarily concern the different shapes of the helium–helium and helium–impurity potentials and the larger mass of the 3He atom, as compared to electronic structure problems. A new integral evaluation procedure is outlined, as well as the necessary modifications to electronic structure codes. Tests against numerically exact calculations for Imp–3He (Imp=Ne, Ar, Kr, Xe, and SF6) complexes show that a modest set of 15 basis functions provides accurate and converged results. Calculations for the lowest triplet state of the SF6(3He)2 cluster, where fermionic statistics comes into play in the orbital part of the helium nuclear wave function, are presented. The triplet state is bound by 22 μhartree with respect to dissociation into 3He+SF6–3He. The applicability of the new method to larger systems is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1409355
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  • 4
    Electronic Resource
    Electronic Resource
    Preference of cluster isomers as a result of quantum delocalization: Potential energy surfaces and intermolecular vibrational states of Ne(centered ellipsis)HBr, Ne(centered ellipsis)HI, and HI(Ar)n (n=1–6) (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1539-1548 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intermolecular vibrational states are calculated for Ne(centered ellipsis)HBr, Ne(centered ellipsis)HI, and HI(Ar)n (n=1–6) complexes using potential energy surfaces constructed by accurate ab initio methods. Potentials of rare gas–hydrogen halide clusters exhibit two collinear minima, one corresponding to hydrogen lying between the heavy atoms, and the other to hydrogen facing away from the rare gas atom. The relative depths of the two minima are a result of a subtle balance between polarization and dispersion interactions. Moreover, due to a large quantum delocalization in the hydrogen bending (librational) motion the relevance of a particular stationary point on the potential energy surface is only limited. It is more appropriate to discuss the isomers in terms of vibrationally averaged structures. For Ne(centered ellipsis)HBr the potential minimum and the vibrationally averaged structure correspond to the same isomer with hydrogen between neon and bromine. However, for Ne(centered ellipsis)HI the global minimum corresponds to the Ne–IH collinear geometry, while the vibrationally averaged structure has hydrogen between the heavy atoms. In the case of HI(Ar)n we show that one can flip between the two isomers by adding argon atoms, which reconciles the seemingly contradictory experimental results obtained for the photodissociation of HI(centered ellipsis)Ar on one side, and of large HI(Ar)n clusters on the other side. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333705
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  • 5
    Electronic Resource
    Electronic Resource
    HCl photodissociation on argon clusters: Effects of sequential solvation and librational preexcitation (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10761-10766 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photolysis of the HCl molecule surface solvated on clusters with 2 to 12 argon atoms is investigated by means of quantum molecular dynamics simulations. Two basic questions are addressed: (i) How does the cage effect change upon increasing the size of the cluster, and (ii) how can caging be influenced by an infrared (IR) excitation of HCl hindered rotation (libration) prior to ultraviolet (UV) photolysis. The efficiency of caging is discussed in terms of measurable quantities. In the time domain, temporary populations of the trapped hydrogen atom are monitored, while in the energy domain short-lived vibrational resonances are observed as a fine structure in the hydrogen kinetic energy distribution. While caging is negligible for the smallest clusters, it becomes more efficient upon increasing the cluster size, and for 12 solvent atoms the cage effect is already very strong. Finally, it is shown that while in the ground state the hydrogen atom points essentially toward the rare gas cluster, in excited librational states hydrogen is directed mostly away from argon atoms. As a consequence, caging of the photodissociating hydrogen atom in the case of a surface solvated HCl molecule can be efficiently "turned off" by librational preexcitation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481720
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  • 6
    Electronic Resource
    Electronic Resource
    Quantum dynamics of large polyatomic systems using a classically based separable potential method (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6046-6056 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method for approximate solution of the time-dependent vibrational Schrödinger equation, applicable to extended molecular systems, is presented. The new method is essentially an approximate time-dependent quantization of classical dynamics. A molecular dynamics simulation is used to obtain a separable, effective time-dependent potential for each mode, that implicitly includes also the effects of all the other modes on this degree of freedom. A time-dependent wave packet is then propagated separately for each mode, using the corresponding effective potential. The new approximation is valid for short time scale processes only, but it is easily applicable to large realistic systems. Test calculations against exact quantum and time-dependent self-consistent field (TDSCF) results are carried out for two examples; photodissociation of HI in the collinear Xe...HI cluster, and electron photodetachment from the collinear Ar...I−...Ar cluster. For illustration, the new scheme is also applied to photodetachment from large linear clusters Arn...I−...Arn (n=2–8) and the results are discussed. For the test systems, the results of the new method are virtually identical to those following from the computationally much more demanding TDSCF approach, and they are in excellent agreement with the exact results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469339
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum dynamics of many-atom systems by the classically based separable potential (CSP) method: Calculations for I−(Ar)12 in full dimensionality (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8855-8864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recently developed method for time-dependent quantum simulations of large systems on short time scales is applied to the dynamics following electron photodetachment from the clusters I−(Ar)2 and I−(Ar)12. The problem is treated in full dimensionality, incorporating all vibrational degrees of freedom, by the classically based separable potential (CSP) approach. This is essentially an approximate time-dependent quantization of classical dynamics: Classical molecular dynamics is used to generate effective, single mode separable time-dependent potentials for each degree of freedom. The quantum dynamics is then propagated separately for each mode, using the effective potentials that implicitly include effects such as energy transfer between the modes. In the current application of the CSP method we calculate properties relevant for the interpretation of spectroscopies, such as correlation functions of wave packets, as well as time-dependent atom–atom distribution functions, pertinent to future diffraction experiments using ultrafast pulses. The insight obtained from the quantum dynamics of these clusters is discussed. In particular, light is thrown on the differences in the dynamics associated with the system landing on the three different electronic surfaces of the neutral I(2P)⋅(Ar)n system. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468939
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  • 8
    Electronic Resource
    Electronic Resource
    Association and dissociation of nonpolar and polar van der Waals pairs in water. Manifestation of the hydrophobic and hydrophilic effect (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 1328-1332 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100055a046
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum dynamics simulations of nonadiabatic processes in many-atom systems: Photoexcited Ba(Ar)10 and Ba(Ar)20 clusters (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5803-5814 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum simulations are reported for the dynamics following the photoexcitation Ba(1S)→Ba(1P) in Ba(Ar)10 and Ba(Ar)20 clusters. The evolution in time is studied in a framework that treats quantum-mechanically all the coupled degrees of freedom. The focus is on the role of nonadiabatic transitions between the three adiabatic surfaces corresponding to the P states of the Ba atom. The time scales of electronic relaxation and of electronic depolarization (orbital reorientation) are computed, and the competition between adiabatic and nonadiabatic effects is assessed. The calculations are carried out by a new scheme that extends the recent classically based separable potential method. Semiclassical surface-hopping simulations are used to produce effective single-mode potentials on which nuclear "orbitals'' are then generated. The full wave packet is constructed from the electronic states involved, and from these nuclear wave functions. Among the main results we find that nonadiabatic transitions become appreciable around 1 ps after photoexcitation, and they are stronger in the smaller cluster. Comparing Tully's semiclassical method with the quantum simulations, good qualitative agreement is found. Quantitatively, the semiclassical predictions for the electronic states branching rations deviate from the quantum results roughly by a factor of 2 after 1 ps. In the smaller cluster direct dissociation of the Ba atom dominates over energy redistribution within the cluster, the opposite being true for the large system. This example demonstrates the feasibility of quantum simulations of nonadiabatic processes in large systems with the new method. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471312
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrafast quantum dynamics and resonance Raman spectroscopy of photoexcited I2(B) in large argon and xenon clusters (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9332-9339 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The early quantum dynamics following the B(3Π0u+)←X photoexcitation of I2 in large rare gas clusters is studied and the resonance Raman spectrum of these systems is calculated by a novel time-dependent quantum mechanical simulation approach. The method used is the classically based separable potential (CSP) approximation, in which classical molecular dynamics simulations are used in a first step to determine an effective time-dependent separable potential for each mode, then followed by quantum wavepacket calculations using these potentials. In the simulations for I2(Ar)n and I2(Xe)n, with n=17, 47, all the modes are treated quantum mechanically. The Raman overtone intensities are computed from the multidimensional time-dependent wavepacket for each system, and the results are compared with experimental data on I2 in Ar matrices and in liquid Xe. The main findings include: (i) Due to wavepacket dephasing effects the Raman spectra are determined well before the iodine atoms hit the rare gas "wall'' at about 80 fs after photoexcitation. (ii) No recurrencies are found in the correlation functions for I2(Ar)n. A very weak recurrence event is found for I2(Xe)n. (iii) The simulations for I2(Ar)17 (first solvation layer) and for I2(Ar)47 (second solvation shell) show differences corresponding to moderate cluster size effects on the Raman spectra. (iv) It is estimated that coupling to the B″(1Π1u) state or to the a(1g) state have a small effect on the Raman intensities. (v) For I2(Ar)47, the results are in very good quantitative agreement with I2/Ar matrix experiments. The I2(Xe)n results are in qualitative agreement with experiments on I2 in liquid Xe. The reported calculations represent a first modeling of resonance Raman spectra by quantum dynamical simulations that include all degrees of freedom in large systems, and they demonstrate the power of the CSP method in this respect. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471678
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