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  • 1995-1999  (24)
  • 1
    Electronic Resource
    Electronic Resource
    A quasiclassical trajectory study of product state distributions from the CN+H2→HCN+H reaction (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6001-6015 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An extensive quasiclassical trajectory study of the dynamics of the CN+H2→HCN+H reaction has been undertaken on two of the potential energy surfaces reported by ter Horst, Schatz, and Harding [J. Chem. Phys. 105, 558 (1996)] with the goal of converging product state distributions. The effect of zero-point energy violations on the behavior of the reactive cross section near threshold has been examined leading to an improved estimate of the thermal rate constant on ter Horst–Schatz–Harding potential energy surface 3 (3.01±0.24×10−14 cm3/s at 300 K). The calculated HCN vibrational product state distribution is not statistical and exhibits a systematic over population in the stretching vibrations of the ground state bend manifold indicating that the –C–N does not behave like a "spectator bond" in this reaction. There is also significant population in modes with bending excitation, but these vibrations are under populated relative to prior statistical expectations. The sensitivity of the distribution on the size of the barrier and its location in the entrance channel has been undertaken by comparing results on the ter Horst–Schatz–Harding potential energy surfaces 2 and 3. Similar to the case of exoergic atom-diatom reactions, it is found that the earlier barrier on ter Horst–Schatz–Harding potential energy surface 3 gives rise to more excitation in the –C–H stretching vibration. The rotational distributions of the HCN product appear similar to the thermal distribution of CN reagents from which they are born indicating that the abstraction of the light H atom perturbs the rotational motion of the cyano radical very little. The dependence of the average HCN rotational quantum number, 〈J〉, on the bending quantum number, v2, exhibits an interesting alternation such that the points for even values of v2 are larger than those for odd. There is a corresponding alternation in the dependence of the average scattering angle, 〈θ〉, on v2 in the opposite sense. These observations suggest that for the odd bending states (which are primarily l=1) the energy diverted into exciting motion perpendicular to the reaction path at the transition state is not available to excite product rotation or to produce reactive trajectories with large impact parameters which lead to small scattering angles. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473264
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of Atomic Fine Structure on Bimolecular Rate Constants: The Cl(2P) + HCl Reaction (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 7522-7529 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100019a038
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A surface-enhanced hyper-Raman and surface-enhanced Raman scattering study of trans-1,2-bis(4-pyridyl)ethylene adsorbed onto silver film over nanosphere electrodes. Vibrational assignments: Experiment and theory (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4313-4323 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present theoretical and experimental studies of the infrared (IR) spectroscopy, normal Raman spectroscopy (NRS), surface-enhanced Raman spectroscopy (SERS), and surface-enhanced hyper-Raman (SEHRS) spectroscopy of trans-1,2-bis(4-pyridyl)ethylene (BPE). This centrosymmetric molecule is expected to have no common Raman and hyper-Raman lines provided that it is not strongly perturbed by adsorption on the surface. The measured SERS spectrum, obtained under electrochemical conditions on Ag film over nanosphere (AgFON) electrodes, shows a well defined C=C stretch band that is not seen in the SEHRS spectrum, but many of the other bands overlap closely. We use ab initio calculations for isolated BPE to assign the spectra, and find excellent agreement between the calculated and measured IR and SERS spectra, and good agreement between the calculated and measured SEHRS spectrum. We find that the apparently overlapping IR, SERS, and SEHRS bands are in fact due to modes that have similar vibrational characteristics but different symmetry. Our results indicate that SEHRS spectra are consistent with the expected (three photon) selection rules and intensities. This rules out an alternative mechanism in which the observed spectrum arises from surface second harmonic generation (SHG) followed by SERS excited at the second harmonic frequency. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471241
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum dynamics of a planar model for the complex forming OH+CO→H+CO2 reaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8807-8817 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quantum dynamics of three and four degrees-of-freedom planar models of the OH+CO→H+CO2 reaction are discussed. These computationally intensive calculations, which are carried out on a scalable parallel computer, illustrate the role of HOCO reaction intermediates or scattering resonances. The results are contrasted with previous two and three degrees-of-freedom quantum results, as well as with two, three, four, and six degrees-of-freedom quasiclassical trajectory calculations. While our quantum calculations are restricted to total angular momentum J=0, it is possible to estimate the thermal rate constant using a J-shifting approximation, and to make comparison with experiment and previous full-dimensional classical trajectory results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468934
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  • 5
    Electronic Resource
    Electronic Resource
    Discrete dipole approximation for calculating extinction and Raman intensities for small particles with arbitrary shapes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 869-875 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a discrete dipole approximation (DDA) method to determine extinction and Raman intensities for small metal particles of arbitrary shape. The Raman intensity calculation involves evaluation of surface electromagnetic fields, and thus is relevant to surface enhanced Raman scattering (SERS) intensities. We demonstrate convergence of the method by considering light absorption and scattering from an isolated spheroid, from an isolated tetrahedron, from two coupled spheroids, and from a spheroid on a flat surface. We also examine comparisons with traditional T-matrix methods. Extensions and simplifications of the method in studies of clusters and arrays of particles are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469787
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  • 6
    Electronic Resource
    Electronic Resource
    Global potential energy surfaces for the lowest 1A', 3A‘, and 1A‘ states of HNO (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 774-783 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present global ab initio potential energy surfaces for the three lowest energy 1A', 3A‘, and 1A‘ surfaces of HNO. These surfaces are the lowest three states of the HNO and HON molecules, and they correlate to the ground electronic states of H+NO and O+NH. In addition, the 3A‘ surface correlates to the ground state of N+OH. The surfaces are based on approximately 800 ab initio calculations that were done using an internally contracted multireference configuration interaction calculation with a large basis set. The ab initio points were fit to a combination of Morse and spline functions in each of the three possible Jacobi coordinates, and the resulting splines were smoothly switched together, and combined with other functions to yield globally defined potentials. Properties of the HNO and HON minima and dissociation energies on these potentials are in good agreement with previous high quality calculations. The N+OH and O+NH reactions are found to have no barriers to formation of HON or HNO, respectively. Isomerization of HON to HNO involves barriers that are higher than the HON dissociation barrier on the singlet surfaces but not on the triplet surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469191
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  • 7
    Electronic Resource
    Electronic Resource
    A theoretical study of the NH+NO reaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6696-6705 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a quasiclassical trajectory study of the NH+NO reaction using a global potential energy surface that is capable of describing branching to the H+N2O and OH+N2 products after initial formation of a HNNO intermediate complex. The surface is based on a many-body expansion wherein fragment potentials for the species N2H, HNO, and N2O are incorporated, using either previously developed potentials, or in the case of N2O, a newly developed potential. The three-body parts of these fragment potentials are damped in the four-body region to provide a zeroth order four-body surface, and then additional four-body terms and mapping transformations are applied to make the final four-body potential match the results of ab initio calculations for eight important HNNO stationary points (minima and saddle points) and for several reaction paths. In addition to this "best fit'' surface (surface I), a second surface (surface II) is developed in which the ordering of the saddle points leading to formation of H+N2O and OH+N2 is reversed, and the energy release during 1,3 hydrogen migration is modified so that the N–N stretch experiences smaller distortions from N2 equilibrium during the reaction leading to OH+N2. Quasiclassical trajectory results on surface I show generally good correspondence with experiment, with a branching fraction of 13±3% for the formation of OH+N2 at 300 K, and relatively low OH and N2 vibration/rotation excitation. The results on surface II are similar with respect to both branching and energy partitioning, indicating relatively weak sensitivity of the results of key features of the surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469143
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  • 8
    Electronic Resource
    Electronic Resource
    Quasiclassical trajectory studies of N+OH, O+NH, and H+NO collisions using global ab initio potential energy surfaces (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 784-791 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a quasiclassical trajectory study of the collisions which occur on the 1A', 3A‘, and 1A‘ potential surfaces of HNO using recently developed global potential surfaces that were derived from ab initio calculations. Each of these surfaces was assumed to be uncoupled from the other surfaces for the purposes of the calculations, and the appropriate statistical average of electronic states for each process was calculated. For N+OH and O+NH, we specifically studied reactive collisions which give H+NO as products, and we also studied the production of N+OH from O+NH. Overall rate constants calculated for either N+OH or O+NH are in good agreement with most experiments, and in addition, the product NO vibrational distribution from the N+OH reaction is in good correspondence with recent measurements, revealing modest excitation that is close to what would be expected from a statistical distribution. For O+NH, the calculated NO vibrational distributions are much hotter than statistical, in apparent disagreement with recent measurements. However, a careful analysis of limitations on the measurements due to spectral interference and to collisional relaxation indicates that it is not possible to say if theory and experiment are at odds for this reaction. We find a significant cross section for O+NH→N+OH on the 3A‘ surface (roughly 5% of the total reactive cross section, independent of energy), and this leads to rate constants at low temperatures that are orders of magnitude higher at low temperature than estimates made earlier based on H atom abstraction on the 5Π surface.The mechanism of this reaction is found to involve three steps: addition to form HNO, isomerization to HON, and dissociation to produce N+OH. We have also studied nonreactive vibrational and rotational excitation in H+NO collisions, and we obtain distributions that are somewhat closer to experiment than obtained in previous theoretical studies, although there are still points of disagreement. We find that reactive H+NO→N+OH collisions have absolute cross sections and average NO rotational excitation that are in excellent agreement with recent fast H atom measurements. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469192
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  • 9
    Electronic Resource
    Electronic Resource
    Complex angular momentum analysis of resonance scattering in the Cl+HCl→ClH+Cl reaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5979-5998 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonance effects in the differential cross sections of the Cl+HCl(v,j)→ClH(v′,j′)+Cl reaction are analyzed using Regge pole and complex angular momentum (CAM) techniques. This is the first detailed application of CAM theory to reactive molecular scattering. The rovibrational transitions studied are v=1, j=5→v′=0, j′=15, and v=1, j=5→v′=1, j′=5 at total energies E=0.66, 0.68, 0.70 eV. The CAM theory expresses the scattering amplitude as a background subamplitude plus a pole subamplitude. The uniform (and nonuniform) semiclassical evaluation of the background subamplitude is discussed. It is necessary to include explicitly the resonance Regge pole in the semiclassical theory because it has a small imaginary part. We derive a new generic semiclassical formula, involving the complementary error function for the resonance angular scattering. The position and residue of the resonance Regge pole at each E are extracted numerically from scattering matrix elements calculated by the centrifugal sudden hyperspherical (CSH) quantum scattering method. There is good agreement between the semiclassical CAM and CSH angular distributions. However, the latter involve summing a partial wave (PW) series with a large number of numerically significant terms—as a result the PW computations provide no physical insight. We also show that a simple semiclassical optical model becomes inaccurate when the rotational period of the ClHCl complex is comparable to the resonance lifetime. We derive a new "sticky'' optical model which allows for rotation of the complex. All our calculations use the Bondi–Connor–Manz–Römelt semiempirical potential energy surface. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470427
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  • 10
    Electronic Resource
    Electronic Resource
    Quasiclassical Trajectory Studies of State-Resolved Bimolecular Reactions: Vibrational Distributions in Triatomic Products (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 516-524 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100002a012
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