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  • 1
    Electronic Resource
    Electronic Resource
    Calculation of expectation values of molecular systems using diffusion Monte Carlo in conjunction with the finite field method (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6353-6355 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A scheme employing the finite field method is proposed for extracting expectation values of molecular properties from diffusion Monte Carlo calculations. The method enables calculation of expectation values of nonlocal operators, such as kinetic energies of molecular components of the system. The method is demonstrated for the H2O...N2 cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468388
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  • 2
    Electronic Resource
    Electronic Resource
    Coupled states calculations on vibrational relaxation in He+CO2(0110) and He+CO (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 802-812 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Computations of vibrational relaxation rate coefficients for He+CO2 (0110) and He+CO (ν=1) over the temperature range 100–300 K are reported. The calculations used the quantum mechanical coupled-channel method for vibrations and the coupled states approximation (CSA) for rotations. These calculations were used to test the accuracy of the vibrationally close coupled, rotationally infinite order sudden approximation (VCC-IOSA) and a semiclassical method. For He+CO2, the VCC-IOSA results compare very well with those obtained using the CSA, while the agreement is not so good for He+CO. This is because CO has a much larger rotational constant and vibrational frequency than CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452282
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer in collisions of He atoms with para-difluorobenzene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 813-821 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy transfer in the three-dimensional collisions of He atoms with para-difluorobenzene (pDFB) has been studied theoretically. A quantum-mechanical scattering method has been employed which uses the close-coupling method for the molecular vibrations and the infinite-order-sudden approximation for rotational motion. Both V–T and V–V processes are studied. The normal mode coefficients for pDFB were obtained from an SCF gradient program. The computations showed a strong propensity for excitation and relaxation of the v30 vibrational mode, which is the mode of lowest frequency. This finding is in agreement with molecular beam experiments of Gentry and co-workers, and laser-fluorescence measurements of Parmenter and co-workers. When the different vibrational modes were given the same frequency in the calculations, modes involving atomic displacements out of the molecular plane had distinctly larger vibrational excitation cross sections than those for in-plane modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452283
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  • 4
    Electronic Resource
    Electronic Resource
    Method for the determination of parametric potential energy surfaces by the direct inversion of inelastic scattering data (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4470-4475 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A direct method is described for inverting inelastic scattering data to obtain parameters in potential energy surfaces. A scattering perturbation technique is adapted to obtain a set of equations for the parameters. These equations are solved iteratively by a repeated solution of the close-coupled equations. The technique is used to determine C6 coefficients in pair potentials for He+CH3F by inverting experimental vibrational relaxation rate constant data. The azimuthal and vibrational close-coupling, rotational infinite-order sudden method is used in these computations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449014
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  • 5
    Electronic Resource
    Electronic Resource
    A theory for the photodissociation of polyatomic molecules, with application to CF3I (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 4288-4298 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is described for calculating photodissociation spectra for polyatomic molecules larger than triatomics. The general method combines the vibrational close-coupling, rotational infinite-order-sudden approximation with the technique of Kulander and Light for calculating photodissociation integrals. The three-dimensional theory enables several vibrational states in the polyatomic photofragments to be coupled together and also allows for initial vibrational and rotational excitation in the parent molecule. The method has been applied to the CF3I→CF3+I (2P1/2) photodissociation process for the radiation frequency range 32 000–42 000 cm−1. Cross sections are reported for CF3I in the ground vibrational state, and also with C–I stretching and bending modes excited initially. Considerable vibrational excitation in the CF3 photofragments is obtained in the calculations at higher frequencies, a finding that is in agreement with experimental measurements. There is a marked preferential population of CF3 combination bands involving simultaneous excitation of both the v1 and v2 vibrational levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450051
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of N2 by collision with He atoms (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3788-3797 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quantum mechanical study of vibrational relaxation in the collision of N2 with 3He and 4He is reported. An ab initio potential energy surface has been computed using the coupled electron pair approximation with an extended basis set. Cross sections for v=1 → 0 vibrational relaxation have been calculated on this surface by using the centrifugal sudden approximation (CSA). The calculated vibrational relaxation rate coefficients show a very encouraging agreement with those measured in laser fluorescence experiments for the temperature range 82–291 K. Over this temperature range the rate coefficients increase by a factor close to 100. The CSA computations are also used to test the accuracy of the vibrational close coupling, rotational infinite order sudden, and the breathing sphere approximations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450089
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  • 7
    Electronic Resource
    Electronic Resource
    Reactions of O(3P) with saturated hydrocarbons: Vibrationally adiabatic distorted wave calculations of product rotational distributions for two triatomic model reactions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2620-2623 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally adiabatic distorted wave (VADW) calculations of product rotational distributions have been performed for the heavy+light–heavy atom reaction O(3P)+HR → OH(v', j')+R, where for v'=0, RH=neopentane=C(CH3)4, and for v'=1, RH=isobutane=(CH3)3CH. Extended London–Eyring–Polanyi–Sato potential energy surfaces are used, with R treated as a structureless particle. It is shown that plotting the rotational distributions against the rotational energy of OH (experimental and theoretical) is a better procedure than just using the rotational quantum number. Good agreement is obtained with experimental rotational distributions and with the results of quasiclassical trajectory calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450332
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  • 8
    Electronic Resource
    Electronic Resource
    Close-coupling calculations on the H+BrH→HBr+H reaction in three dimensions (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1685-1692 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Close-coupling calculations on the H+BrH(v=0, j)→HBr(v=0, j′)+H reaction in three dimensions are reported. Cross sections have been computed for an energy range sufficient to give a converged rate constant at room temperature. The results are used to test the accuracy of sudden approximations and a variational transition state theory with tunneling correction. It is found that these approximate theories slightly overestimate the reaction rate constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449355
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  • 9
    Electronic Resource
    Electronic Resource
    Infinite order sudden calculation of Raman Q-branch linewidths for H2O+H2O (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1037-1048 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infinite order sudden (IOS) approximation is extended to calculate rate constants for rotationally inelastic scattering between two H2O molecules. A modified version of the breathing sphere (BS) approximation, which has previously been shown to work reasonably well for N2+N2 rotationally inelastic scattering, is also extended to H2O+H2O scattering. The rate constants obtained using both approximations are used to determine Raman Q-branch spectral linewidths. In order to calculate such linewidths, it is necessary to sum the rate constants for any initial rotational level over all final inelastic rotational levels. While the IOS linewidths are in reasonable agreement with experiment over a range of temperatures, the IOS-BS linewidths are much too small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461131
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  • 10
    Electronic Resource
    Electronic Resource
    Rovibrational spectra of open-shell van der Waals complexes: Ar–OH(X 2Π) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4149-4160 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of Ar(1S0)–OH(X 2Π) has been predicted using an ab initio potential-energy surface. We assume that the electronic spin and orbital angular momenta remain coupled to the rotational motion of the diatom in a van der Waals complex. The rovibrational energies and wave functions are calculated using a basis-set method involving expansion of the rovibrational wave function in terms of a product basis of optimized radial and angular wave functions. Unusual features are observed due to the nonzero electronic angular momentum of the diatom in the rovibrational levels. The effect of deuterium substitution on the predicted spectra has also been studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460648
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