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  • 1
    Electronic Resource
    Electronic Resource
    Perturbative calculations of vibrational (J=0) energy levels of linear molecules in normal coordinate representations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3476-3487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Canonical Van Vleck perturbation theory is used to transform curvilinear and rectilinear normal coordinate vibrational Hamiltonians of HCN, C2H2, and CO2 to block-diagonal effective Hamiltonians. Accurate energies as high as 11 000 cm−1 above the zero point are reported for all three molecules. In the absence of off-diagonal coupling terms in the effective Hamiltonians, these two coordinate systems yield identical perturbative expansions for the vibrational energies. Only when coupling terms are introduced do differences between the calculated energies in the two representations become apparent. In CO2, where there is pronounced configuration interaction between nearly degenerate states, we find that the perturbative energies obtained from the curvilinear normal coordinate Hamiltonian are converging significantly faster than those obtained in the rectilinear normal coordinate representation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460850
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  • 2
    Electronic Resource
    Electronic Resource
    Perturbative approaches to highly excited molecular vibrations of H2O, D2O, and HDO (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1893-1901 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular vibrations of water are studied using Van Vleck perturbation theory. In these calculations, the OH stretches are expressed in terms of the Morse coordinate, yi =[1−exp(−αri)]/α, and its conjugate momentum, while the bend is treated in a traditional manner. Nearly degenerate perturbative calculations are presented for bond and normal-mode representations. The eigenvalues agree well with those obtained variationally. The coefficients of the perturbatively derived, effective Hamiltonians are compared to those of spectroscopic Hamiltonians with similar structural forms. The former are derived from the potential of Halonen and Carrington [J. Chem. Phys. 88, 4171 (1988)], whereas the latter are treated as spectral fitting parameters. The fit parameters are accurately reproduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458071
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo studies of the structure and spectroscopy of NenOH (A˜ 2Σ+, n=1–4) van der Waals complexes (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 10278-10287 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Adiabatic rigid-body diffusion Monte Carlo is used to study the structure and spectroscopy of complexes of OH(A˜ 2Σ+) with several neon atoms. Although the potential energy surfaces for these systems have many low-lying minima, the ground state wave functions are localized in the global minimum. This trend is found to persist in the first few vibrationally excited states of Ne2OH/D. Low-lying vibrational states that are localized in the potential minimum that corresponds to the linear Ne–OH/D–Ne configuration of the complex are also found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372185
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  • 4
    Electronic Resource
    Electronic Resource
    Multiple configuration quantum/classical treatments of reaction dynamics (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 10605-10614 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The accuracy of quantum/classical approaches for studies of reaction dynamics is investigated through simulations of the collinear and J=0 dynamics of the O(3P)+HCl reaction on two potential surfaces. The results of classical and two types of quantum/classical treatments of this reaction are compared to the results of quantum wave packet simulations. It is found that the accuracy of the single configuration quantum/classical treatment is sensitive to features of the potential surface. Most of this sensitivity is removed when a second configuration is introduced. For collision energies below 0.8 eV, the multiple configuration quantum/classical treatment provides reaction probabilities and product state distributions that are in good agreement with the results of the corresponding quantum simulation. The agreement deteriorates at higher collision energies, but here the agreement between the quantum and classical results is quite good. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1317549
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical studies of the X˜ 2Π and A˜ 2Σ+ states of the He⋅OH and Ne⋅OH complexes (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5736-5749 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces for the X˜ 2Π and A˜ 2Σ+ states of the He⋅OH and Ne⋅OH complexes have been developed, using the restricted open-shell coupled cluster [RCCSD(T)] method. These potentials have been used to calculate rotation-vibration energies for both electronic states of these complexes and their deuterated analogs. Good agreement with the available experimental vibrational energies and rotational constants is obtained. In spite of being relatively weakly bound, the vibrational eigenstates for both electronic states of these species display significant deviations from the simple zero-order free-rotor/anharmonic oscillator limit, leading to potentially rich spectra. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290605
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  • 6
    Electronic Resource
    Electronic Resource
    A quantitative approximation for the quantum dynamics of hydrogen transfer: Transition state dynamics and decay in ClHCl− (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1975-1987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general method for studying transition state spectroscopy and dynamics in hydrogen atom transfer reactions is presented. This approach is based on the time-dependent self-consistent field (TDSCF) approximation and is applied to a study of the ClHCl− photodetachment experiments of Metz et al. [Metz et al., J. Chem. Phys. 88, 1463 (1988)]. Comparison of results of exact time-dependent and TDSCF calculations are made for collinear and three-dimensional (J=0) approximations for the quantum dynamics. When ClHCl is constrained to be collinear, the TDSCF calculation overcorrelates the motions in the H atom displacement and ClCl extension coordinates. This results in relatively poor agreement with the exact result for many properties of the wave function. In contrast, when the system is propagated in the three vibrational coordinates of the system, the transition state dynamics are effectively over much more rapidly. Consequently, the TDSCF approximation yields results of very good quantitative accuracy over the time required for most of the wave function to decay off of the transition state. Comparison is also made between the wave function that results from the exact propagation and from TDSCF when the wave function in the ClCl stretch coordinate is approximated by a Gaussian wave packet. Here the magnitude of the overlap between the two TDSCF wave functions in the H atom coordinates, for quantum and semiclassical propagations of the wave function in the ClCl distance coordinate, is greater than 0.98 over the time of the propagations. These TDSCF calculations are repeated for a wave function that is approximated by a product of a two-dimensional wave function in the hydrogen atom coordinates and a one-dimensional wave function in the ClCl extension coordinate and even better quantitative agreement with the exact propagation is achieved. The success of this method for studying ClHCl gives us confidence that TDSCF will provide a general powerful tool for studies of hydrogen and proton transfer reactions in large systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467707
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo studies of small B(H2)n clusters (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2577-2591 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and stability of clusters of a boron atom with one to eight H2 molecules is investigated. For the simplest BH2 clusters, the lowest ab initio adiabatic potentials for o-H2 and p-H2 interacting with a boron atom are used. For the larger clusters (n=2–8), the p-H2 is treated as a sphere, and the total potential is taken to be the sum of pairwise additive B–H2 and H2–H2 interactions which include, in the former case, an anisotropy due to the orientation of the unpaired B 2p electron. This electronic interaction is considerably more attractive when H2 approaches the B atom in a plane perpendicular to the orientation of the 2p orbital. The local and global minima on these potential surfaces were located and diffusion quantum Monte Carlo simulations were used to determine the energies and properties of the ground state wave functions for these B–(H2)n clusters. For the B(H2) cluster, a comparison is made with the results of variational calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468432
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  • 8
    Electronic Resource
    Electronic Resource
    An empirical potential energy surface for the Ne–OH/D complexes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10053-10060 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An empirical potential energy surface has been developed for the Ne–OH/D complexes from the experimentally observed vibrational and rotational energy levels with the results of ab initio calculations being used to provide initial estimates of the values of the parameters in the empirical potential. To determine the final surface a reassignment of the A˜ 2Σ+–X˜ 2Π bend–stretch combination bands, to fundamentals of the bend, was made, and the experimental data for both the Ne–OH and Ne–OD complexes were fit simultaneously due to the small number of available values. The vibrational energies and rotational constants resulting from the fit surface are within 0.2 and 0.0013 cm−1, respectively, of the experimental values. The details of the potential energy surface are discussed in relationship to those of other inert gas complexes containing OH and SH, as well as HCl and HF. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480391
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  • 9
    Electronic Resource
    Electronic Resource
    Structure and spectroscopy of NenSH (A˜ 2Σ+) complexes using adiabatic diffusion Monte Carlo (ADMC) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9203-9212 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Adiabatic rigid body diffusion Monte Carlo techniques are used to investigate the structure and spectroscopy of complexes of one to four neon atoms with SH (A˜ 2Σ+). While these systems contain multiple low-lying minima, the ground state wave functions are well described by a neon cluster weakly interacting with SH. This structure persists in low-lying excited states, in the case of complexes of two neon atoms with SH or SD. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479834
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  • 10
    Electronic Resource
    Electronic Resource
    Rotation–vibration interactions in highly excited states of SO2 and H2CO (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7449-7465 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Canonical Van Vleck perturbation theory (CVPT) is used to investigate rotation–vibration mixing of highly excited vibrational states of SO2 and H2CO. For SO2 we find a nearly complete separation of the rotational and vibrational degrees of freedom, even for J=12 and Evib=11 000 cm−1. In contrast, for H2CO we observe extensive mixing between rotational and vibrational degrees of freedom at similar rotational excitation but with Evib=8000 cm−1. Although a-axis Coriolis coupling is pronounced, b- and c-axis Coriolis couplings play an important additional role in mixing states with different Ka quantum numbers. The implementation of CVPT, the choice of internal coordinates, and the convergence of the results are discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461371
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