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  • 1985-1989  (7)
  • 1986  (7)
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  • 1985-1989  (7)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Quantum studies of inelastic collisions of O2(X 3Σ−g) with He: Polarization effects and collisional propensity rules (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2726-2737 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate rotationally inelastic cross sections of O2(X 3Σ−g) with He at a collision energy of 27 meV. Theoretical cross sections obtained from close-coupled (CC) calculations are compared with results from the infinite-order sudden (IOS) approximation. Both the CC and IOS fine-structure state-resolved cross sections exhibit a strong ΔN=ΔJ Fi conserving collisional propensity. An analysis of the general expression for state-resolved cross sections in terms of spin-independent tensor opacities clearly establishes, without the introduction of dynamical approximations, the direct connection between this propensity rule and the collisional propensity for the conservation of the orientation of the nuclear rotational angular momentum vector N. In the low-N limit, Fi changing O2–He collisions are much more strongly depolarizing than collisions that conserve the Fi symmetry level. This enhanced collisional depolarization of an initial distribution of the total molecular angular momentum vector J is related to the collisional reorientation of N that must occur in Fi changing transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451029
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Rotationally inelastic collisions between a molecule in a 2Σ electronic state and a 2S atom: Sudden factorization, scaling, and symmetry relations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1859-1865 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sudden factorization and scaling relations are developed for the scattering of molecules in 2Σ electronic states by open-shell 2S atoms, with particular emphasis given to the influence of the open-shell character of the atomic perturber. The molecule-state-resolved cross sections are expressed as a sum of spin-independent and spin-correlated terms. Both terms can be expressed as a weighted sum of spin-free tensor opacities. In the sudden limit the tensor opacities satisfy factorization relations formally equivalent to those first derived for 1Σ–1S collision systems. However, in the collision of two open-shell species these dynamical factors cannot be identified with inelastic scattering off a single adiabatic potential energy surface. The breakdown in the scaling and symmetry relations, which are valid in the energy sudden limit, for 2Σ-state molecules scattering off closed-shell targets provides a qualitative measure of the strength of the electrostatic exchange forces which arise from the open-shell nature of both the molecule and the atomic target.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451188
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The infinite-order sudden approximation for collisions involving molecules in Π electronic states: A new derivation and calculations of rotationally inelastic cross sections for NO(X 2Π)+He and Ar (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5652-5659 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new derivation is presented of the infinite-order sudden (IOS) approximation for rotationally inelastic collisions of a diatomic molecule in a Π electronic state with a closed-shell atom. This derivation clearly demonstrates the connection between the two sudden S functions for scattering off the adiabatic potential surfaces of A' and A‘ symmetry, which would arise from an ab initio calculation on an atom+Π-state molecule system, and the S-matrix elements in a diabatic basis, which are required in the quantum treatment of the collision dynamics. Coupled-states and IOS calculations were carried out for collisions of NO(X 2Π) with He and Ar, based on the electron gas potential surface of Nielson, Parker, and Pack [J. Chem. Phys. 66, 1396 (1977)], at total energies of 63, 150, and 300 meV. The IOS approximation is not reliable for collisions of NO with Ar, even at the highest collision energy considered here. However, for collisions with He at 150 and 300 meV, the IOS approximation is nearly quantitative for transitions both within and between the Ω=1/2 and Ω=3/2 manifolds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451578
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Theory of Stark spectroscopy of molecules in 1Π electronic states: Coherence effects and quantum beats (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 134-145 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A density operator formalism is used to describe the fluorescence of a molecule in a 1Π electronic state in a static electric field under both pulsed and cw excitation. Coherences can be created both between M levels as well as between the e and f Λ-doublet levels. Explicit solution of the generalized master equation allows the development of general expressions for the excited state density matrix elements, under conditions where collisions, hyperfine structure, optical pumping, and optical saturation are ignored. Simple expressions are obtained for the fluorescence intensities, valid at high J and whenever the Stark shifts are significantly smaller than zero-field Λ-doublet splitting. A simulation study of the expected quantum beat patterns is reported based on the parameters reported by Mandich, Gaebe, and Gottscho [J. Chem. Phys. 83, 3349 (1985)] in their experimental study of BCl(A1Π). Attention is focused on the extent to which quantum beat effects will be obscured by the finite widths of the laser excitation pulse and detector response functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451649
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    On the physical origin of propensity rules in collisions involving molecules in 2Σ electronic states (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3049-3058 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general quantum treatment of the collision dynamics of 2S+1Σ-state diatomic molecules is developed, with particular emphasis given to the physical origin of the collisional propensity for conservation of the e/f molecular symmetry label. State-resolved integral cross sections are expressed as a weighted sum of tensor opacities which are related to the probability that a collision will reorient the nuclear rotational angular momentum vector. Previous derivations of the propensity rules for collisions of 2S+1Σ-state diatomic molecules were restricted to the sudden or Born approximations. Here a general derivation is developed that is free of dynamical approximations, and that clearly establishes the direct connection between the observed propensity for the conservation of the e/f molecular symmetry and the collisional propensity for the conservation of the orientation of the nuclear rotational angular momentum vector. A power-law model suggested by previous semiempirical fits to cross sections for 1Σ+-state molecules is extended to open-shell molecules. This simple model allows us to predict semiquantitatively the degree to which the e/f symmetry index is conserved without performing a full dynamical calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450286
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Rotationally inelastic collisions between a molecule in a 2S+1Σ electronic state and an open-shell target: General quantum analysis and experimental measurement of state-resolved cross sections for CaCl(X 2Σ+)+NO(X 2Σ) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1547-1553 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The general quantum treatment for the scattering of molecules in 2S+1∑ electronic states by open-shell 2S atoms is investigated, with particular emphasis given to the influence of the open-shell character of the atomic perturber on the collisional propensity for conservation of the e/f molecular symmetry index. The molecule-state-resolved cross sections are expressed as a sum of spin-independent and spin-correlated terms. The spin-independent term is formally equivalent to the cross section for state-resolved transitions in a 2S+1∑-state molecule upon collision with a structureless target. The spin-correlated term is due solely to the electrostatic exchange forces arising from the open-shell nature of both the molecule and the atomic target. Recently calculated CaCl(X 2∑+)–Ar cross sections are used to investigate the extent to which e/f conservation depends on the relative magnitudes of these two contributions. Experimental state-to-state rotationally inelastic cross sections for the scattering of CaCl(X 2∑+) by the open-shell NO(X 2∏) molecule are presented and analyzed by means of this formalism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450842
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Collision induced transitions between 2Π and 2Σ states of diatomic molecules: Quantum theory and collisional propensity rules (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 100-113 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop the exact quantum description, free of any dynamical approximations, of rotationally inelastic collision induced transitions between 2Π and 2Σ electronic states of a diatomic molecule. An explicit connection is made between the matrix elements of the electrostatic coupling, described in an asymptotically exact diabatic basis, and the results of an ab initio calculation of the appropriate atom–molecule adiabatic electronic wave functions of A' and A‘ symmetry. Analysis of the quantum close-coupled equations demonstrates that the use of Franck–Condon approximations in the description of E → E energy transfer is unjustified and, furthermore, that in collisions involving homonuclear diatomic molecules the s/a permutation-inversion symmetry of the molecular wave functions will be rigorously conserved. The extension of the infinite-order sudden approximation to electronically inelastic 2Π → 2Σ processes allows us to predict two new collisional propensity rules: (a) When Δ J=0 the cross sections will become vanishingly small for transitions which conserve the e/f symmetry index of the molecular wave function. (b) In a high-J Hund's case (b) limit transitions from either the F1 or F2 2Π-state manifolds will populate only one of the Σ-state spin-doublet levels, consistent with a physical model in which the electronic spin S is a spectator so that the relative orientation of N and S is preserved during the collision.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450831
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    Paper (German National Licenses)
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