The inelastic scattering of /sup 2//Pi/ (case (b)) molecules and an understanding of the differing. lambda. doublet propensities for molecules of. pi. vs. pi. /sup 3/ orbital occupancy
The quantum formalism for the scattering of a diatomic molecule in a /sup 2//Pi/ electronic state which is well described by Hund's case (b) limit is investigated here. For a particular /ital JF//sub /ital i///r arrow//ital J/'/ital F//sup '//sub 1/ transition, quantum interference effects will lead to preferential population of one of the final state ..lambda.. doublet levels. The nonstatistical population of final state ..lambda.. doublet levels arises from an interference between terms in the expansion of the two electrostatic potential energy surfaces, of /ital A/' and /ital A//double prime/ reflection symmetry, which describe the interaction between a molecule in a /Pi/ electronic state and a closed-shell partner. The particular ..lambda.. doublet level preferred is opposite for molecules of ..pi../sup 1/ vs ..pi../sup 3/ electron occupancy. The physical origin of this reversal in the ..lambda.. doublet propensity is a direct reflection of the fact that for the former the /ital A/' potential surface is more repulsive since the sole ..pi.. electron lies in the triatomic plane in this case, whereas for molecules of ..pi../sup 3/ electron occupancy the /ital A/' surface is less repulsive than the /ital A//double prime/ surface since for the /ital A/' surface only one of the three ..pi.. electrons lies in the triatomic plane. The magnitude of these ..lambda.. doublet propensities is illustrated by calculated cross sections for the CH(/ital X/ /sup 2//Pi/)--He system using the /ital ab/ /ital initio/ potential energy surfaces calculated by the Argonne theoretical group, and these cross sections are compared to those of the crossed molecular study of Liu and Macdonald (J. Chem. Phys. /bold 91/, xxxx (1989)). A similar analysis is carried out for collisions of a molecule of ..pi../sup 3/ electron occupancy and is illustrated by inelastic collisions of OH(/ital X//sup 2//Pi/).
- Research Organization:
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218(US); Department of Chemistry, University of Maryland, College Park, Maryland 20742; Gas Phase Chemical Dynamics Group, Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
- OSTI ID:
- 6016631
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 91:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HELIUM
ATOM-MOLECULE COLLISIONS
METHYLENE RADICALS
MOLECULES
INELASTIC SCATTERING
CROSS SECTIONS
ELECTRONIC STRUCTURE
ENERGY-LEVEL TRANSITIONS
ROTATIONAL STATES
ATOM COLLISIONS
COLLISIONS
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FLUIDS
GASES
MOLECULE COLLISIONS
NONMETALS
RADICALS
RARE GASES
SCATTERING
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena