Propensity rules for rotationally inelastic collisions of symmetric top molecules or linear polyatomic molecules with structureless atoms

Journal Article · Sun Aug 15 00:00:00 EDT 1982 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.444037· OSTI ID:5020875

Alexander, M H

Using an asymptotic expansion of the angular momentum coupling coefficients which appear in the infinite-order-sudden formulation of collisions between symmetric top molecules and structureless atoms (S. Green, J. Chem. Phys. 70, 816 (1979)), we demonstrate that in certain cases, transitions which conserve the ''parity index'' of the rotational wave function will be strongly favored over those in which the parity index changes. This propensity rule will apply both to transitions which are inelastic in J but elastic in K, the projection of J along the molecular axis, as well as to transitions which are elastic in J but inelastic in K. Identical propensity rules will emerge within a Born treatment of the collision dynamics. These rules are completely general and independent of the particular form of the atom--molecule potential. The propensity toward conservation of the parity index will also be apparent in collisions of slightly asymmetric tops and l-doubled linear polyatomic molecules. A simple criteria is developed to determine the minimum value of J for which these propensity rules will be valid. Examination of accurate close-coupling and coupled-states cross sections for the NH/sub 3/--He and H/sub 2/CO--He systems confirms the accuracy of the new propensity rules. These rules can be used to predict intensity changes in four-level double resonance experiments; excellent agreement is obtained in a comparison with available experimental data for collisions of both HCN and NH/sub 3/ with He, Ar, Xe, and H/sub 2/.

• Research Organization: Department of Chemistry, University of Maryland, College Park, Maryland 20742
• OSTI ID: 5020875
• Journal Information: J. Chem. Phys.; (United States), Vol. 77:4
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
AMMONIA
ATOM-MOLECULE COLLISIONS
ARGON
HELIUM
HYDROCYANIC ACID
HYDROGEN
XENON
ENERGY-LEVEL TRANSITIONS
ROTATIONAL STATES
ATOM COLLISIONS
COLLISIONS
CYANIDES
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FLUIDS
GASES
HYDRIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
MOLECULE COLLISIONS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
RARE GASES
640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena