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  • 1990-1994  (17)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Rate coefficient expressions for reactions of molecules in 2Π electronic states at low temperatures (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 420-426 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Analytical rate coefficient expressions are derived at low temperatures for the fast reactions of a 2Π molecule with each of a structureless ion, a 2Π molecule, and a 1Σ molecule. The procedure, based on classical capture theory, involves perturbation theory and simple long-range electrostatic potential terms for the various interactions. The open-shell nature of the reactant molecules is fully considered. The predictions made are contrasted with those quoted previously for the equivalent reactions involving 1Σ molecules and interesting differences in the temperature dependencies of the rate coefficient are highlighted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464635
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational predissociation of ArH2O (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8111-8122 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Accurate close-coupling calculations are used to investigate the vibrational predissociation of ArH2O as a function of the overall rotation J of the van der Waals complex. A full vibrational and rotational basis of H2O states is used in the calculation. The potential energy surface is of a form due to Cohen and Saykally and derived from far-infrared spectra, with an additional term to introduce the dependence on the vibrations of H2O. The linewidths calculated in this work show a maximum at J=6 and it is found that Fermi resonances affect dramatically the magnitude of the calculated linewidths. Good agreement with experimentally measured linewidths of Nesbitt and Lascola is achieved and the calculations provide a simple picture for the J dependence of the linewidths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463432
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Reaction rates of ions with dipolar molecules in 2Π electronic states (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1053-1061 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of rate coefficients for the fast reaction of a structureless ion with a dipolar linear molecule in a 2Π electronic state are presented. The rotationally adiabatic capture theory is used together with a simple classical electrostatic potential. An analytical formula is derived for the rate coefficient in the low temperature limit. The reaction of H+3 with OH(X 2Π) is taken as an example. For temperatures less than 90 K, the rate coefficients differ from those calculated for molecules in 1Σ states. The most interesting new prediction is that the rate coefficient for the reaction of a 2Π polar molecule with an ion is proportional to T−1/2 for temperatures close to absolute zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462192
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    Paper (German National Licenses)
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  • 4
    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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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Prediction of the spectrum for excitation of the van der Waals modes in ArHCN (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7666-7675 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A calculation of the spectrum for the excitation of the van der Waals modes in ArHCN is reported. The coupled electron pair approximation is used to compute an ab initio potential energy surface for the interaction of Ar with rigid HCN. The rovibrational bound states for the complex are calculated using a variational coupled-basis set method in which a self-consistent field approach is used to optimize simultaneously the basis sets for both the intermolecular bending and stretching motions in the van der Waals molecule. The calculations are compared with experimental results, including a measurement of the infrared spectrum of ArHCN in the region of the CH stretching vibration. The calculations predict that several bending modes with frequencies less than 20 cm−1 should have excitation intensities large enough to be observed. These low frequency bending modes arise from the small rotational constant of the HCN molecule and are not due to special features of the Ar–HCN potential energy surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459398
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  • 6
    Electronic Resource
    Electronic Resource
    Calculations on the van der Waals spectrum of Ar–tetrazine (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5875-5884 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The van der Waals bound states of Ar–tetrazine are calculated by a method which treats the tetrazine fragment as a rigid rotor, but which is otherwise exact within the Born–Oppenheimer approximation. The results are used to obtain frequencies and intensities for transitions between van der Waals states in the S1←S0 electronic spectrum of the complex. Selection rules for such transitions are derived using permutation–inversion symmetry arguments. The normal rigid molecule selection rules are relaxed due to coupling between the low frequency van der Waals vibrations and the overall rotation of the complex, leading to the possibility of observing single excitation of the nontotally symmetric van der Waals bending modes. Transition intensities for van der Waals stretching excitation are predicted much smaller than experiment and various possible explanations for this disagreement are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458357
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  • 7
    Electronic Resource
    Electronic Resource
    Calculation of van der Waals spectra for H2HF, D2HF, and H2DF (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6334-6349 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Calculations of spectra for the excitation of the van der Waals modes in the weakly bound complexes H2HF, D2HF, and H2DF are reported. An ab initio potential energy surface has been computed using the coupled electron pair approximation with a large basis set. The rovibrational bound states for the complexes are calculated using a variational method. A self-consistent field approach is used to optimize the basis sets for bending and stretching motion in the van der Waals complex. The calculated spectra compare very well with those measured in near-infrared experiments. The computations provide a systematic analysis of the relative stability and rigidity of the different complexes, the very large zero-point energy effects, and the unusual nature of the rovibrational wave functions in these van der Waals molecules. The predicted spectra contain some new bands with surprisingly large intensities that might be detectable in experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458976
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  • 8
    Electronic Resource
    Electronic Resource
    Calculation of the electronic spectrum for Ar–OH (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3367-3378 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We calculate the rovibrational structure for the electronic transition of the Ar–OH complex between the ground and first excited electronic states, which correlate asymptotically with Ar(1S0)+OH(X 2Π) and Ar(1S0)+OH(A 2Σ+), respectively. An ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex. The calculated spectrum is compared with experimental results. In the low-frequency region the spectrum is found to be well ordered and assignment of spectroscopic features in terms of bending and stretching quantum numbers is possible. Close to dissociation, bend–stretch coupling leads to highly mixed states for which such assignments are no longer possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458817
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Rotationally and vibrationally inelastic scattering of glyoxal at E=80 meV (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 287-311 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of quantum calculations on rotationally and vibrationally inelastic scattering of 1Au(S1) trans-glyoxal by H2,He, and Ar(E=80 meV) are presented. For scattering of 00 glyoxal and 72 glyoxal by H2, a quantitative comparison with a recent crossed beam experiment is made. The calculated cross sections for rotationally inelastic scattering are in good agreement with the experimental values, and the trend that σ(72, k=0→72, k') falls off faster with k' than σ(00, k=0→00, k') is reproduced. Our calculations do not reproduce the experimental finding that, for the initial 72 level, the cross sections for the Δv7=−1 and Δv7=+1 transitions are nearly identical. The calculations on 72 glyoxal + He and Ar show important differences with 72 glyoxal + H2 in the competition of rotational excitation with vibrational excitation. Model calculations also presented here yield some interesting trends in the k' dependence of the cross sections σ(00, k=0→x1, k') on the vibrational mode x excited.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459602
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  • 10
    Electronic Resource
    Electronic Resource
    Calculations on vibrational predissociation of Ar–OH (A 2Σ+) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8149-8165 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An R-matrix algorithm is developed for executing vibrational predissociation calculations within the Golden Rule approximation. The algorithm is used to calculate vibrational predissociation linewidths and OH product rotational distributions for the quasibound states of Ar–OH (A2 Σ+, v=1). An ab initio potential energy surface obtained with the coupled electron pair approximation is used in the computations. The theoretical results are compared with experiment. The high anisotropy of the system is found to strongly favor vibrational to rotational energy transfer and the product OH (A2 Σ+ , v=0) molecules are produced in highly excited rotational states. Quasibound states associated with excited bending levels are predicted to dissociate more rapidly than those assigned to the ground bend. For metastable states with the same bending quantum number, linewidths are predicted to decrease with increase in the intermolecular stretching quantum number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461295
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