Propensity rules in rotationally inelastic collisions of diatomic molecules in /sup 3/. sigma. electronic states
The formalism for the treatment of rotationally inelastic collisions of molecules in /sup 3/..sigma.. electronic states is exposed, for the general case of intermediate coupling. The reduced matrix elements of the T operator are expressed in a Hund's case (a) basis. Within the infinite-order-sudden (IOS) limit, the symmetry of the reduced T-matrix elements and the large-J limit of certain vector coupling coefficients can be used to derive several propensity rules bearing on changes in the F/sub i/(i = 1--3) label. In particular, for large J only the F/sub i/ conserving transitions will have large cross sections. From a physical viewpoint this propensity rule implies that the scattering, at least in the IOS limit at large J, is independent of ..sigma.., the spin projection quantum number. The experimental study by Caughey and Crosley (J. Chem. Phys. 71, 736 (1979)) of rotational relaxation in the B /sup 3/..sigma../sub u//sup -/ state of S/sub 2/ confirms our theoretical propensity rules, although the experimental rate constants for the F/sub 1/ ..-->.. F/sub 2/, F/sub 3/ transitions are considerably larger than would be predicted theoretically.
- Research Organization:
- Department of Chemistry, University of Maryland, College Park, Maryland 20742
- OSTI ID:
- 5885379
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 79:1; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
COLLISIONS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
INELASTIC SCATTERING
MATRICES
MATRIX ELEMENTS
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
ROTATIONAL STATES
S MATRIX
SCATTERING
SUDDEN APPROXIMATION