Quantum scattering studies of inelastic collisions of NH( A sup 3. Pi. ) with helium: Fine-structure and. Lambda. -doublet propensities

Journal Article · Tue Oct 01 00:00:00 EDT 1991 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.461792· OSTI ID:5253661

Alexander, M H ^[1]; Dagdigian, P J ^[2]; Lemoine, D ^[3]

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1. Department of Chemistry, University of Maryland, College Park, Maryland (USA)
2. Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland (USA)
3. Laboratoire de Spectroscopie des Molecules Diatomiques, URA 779, Universite de Lille I, Batiment P5, 59655 Villeneuve d'Ascq Cedex (France)

The results of full close-coupled calculations of state-to-state cross sections for rotationally inelastic collisions of NH in its {ital A}{sup 3}{Pi} electronic state with helium, based on the recently calculated {ital ab} {ital initio} potential energy surfaces of Jonas and Staemmler (Z. Phys. D {bold 14}, 143 (1989)), are presented. The calculated {Lambda}-doublet resolved cross sections have been compared with predictions based on formal analyses of the scattering equations both in the Hund's case (a) and (b) limits. For transitions involving low {ital J} levels, a strong propensity toward conservation of the {ital e}/{ital f} label was found, as expected in the case (a) limit. For higher {ital J}, the cross sections connecting related pairs of {Lambda}-doublet levels were found to be unequal, reflecting a quantum mechanical interference between the two potential energy surfaces arising from the interaction of a molecule in a {Lambda}{gt}0 state with a perturber. For transitions connected by even {ital l} terms in the expansion of the potentials, a simple analysis, based on the relative strengths of the {ital l}=2 coupling matrix elements of the electrostatic potential, was found capable of explaining the relative ordering of the cross sections in most cases. A similar success for predicting transitions coupled by odd {ital l} terms in the potential was not found; this reflects the fact that the {ital l}=3 terms are relatively small for the NH({ital A} {sup 3}{Pi})--He interaction. The calculated cross sections for large {ital J} also exhibit a propensity for conservation of the fine-structure label, as expected in the case (b) limit.

• OSTI ID: 5253661
• Journal Information: Journal of Chemical Physics; (United States), Vol. 95:7; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
HELIUM
ATOM-MOLECULE COLLISIONS
NITROGEN HYDRIDES
CROSS SECTIONS
FINE STRUCTURE
INELASTIC SCATTERING
ATOM COLLISIONS
COLLISIONS
ELEMENTS
FLUIDS
GASES
HYDRIDES
HYDROGEN COMPOUNDS
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NONMETALS
RARE GASES
SCATTERING
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena