Sudden theories of rotationally inelastic LiH--HCl and LiH--DCl collisions
The impact parameter sudden approximation is applied to rotationally inelastic collisions between two polar molecules. The transition probabilities can be factored into a sum of squares of angular momentum coupling coefficients multiplied by dynamical factors which are related to coefficients in the expansion of the sudden scattering operator. The evaluation of these dynamical factors is discussed for the case of a potential which consists of the dipole--dipole term as well as both dipole--quadrupole terms in the standard multipole expansion. Even at relatively high collision velocities these long-range potentials will necessitate significant adabatic corrections to the pure sudden approximation, which can be determined by the introduction into the sudden action integral of a ''dephasing frequency'' proportional to the average rotational energy transfer per single quantum transition. The resulting adiabatically corrected sudden (ACS) approximation (M. H. Alexander and A. E. DePristo, J. Chem. Phys. 83, 1499 (1979)) yields a factorization similar to that obtained in the pure SA. The appropriate dynamical factors can be evaluated by a two-dimensional quadrature. ACS and SA calculations are reported for the collision of a LiH molecule with both HCl and DCl at a collision energy of 0.78 eV. The presence of the dipole--quadrupole terms results in an interesting alternance in some of the j/sub a/j/sub b/..-->..j/sub a/'j/sub b/' cross sections, but leads to little change in the total cross section obtained by summing over the final states of the hydrogen halide partner. In a strong resonance effect the magnitude of these summed cross sections for directly coupled dipole transitions (..delta..j/sub a/= +- 1) varies substantially with the initial rotational state of the partner.
- Research Organization:
- Department of Chemistry, University of Maryland, College Park, Maryland 20742
- OSTI ID:
- 6050513
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 71:4; 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
ALKALI METAL COMPOUNDS
COLLISIONS
DEUTERIUM COMPOUNDS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HYDRIDES
HYDROCHLORIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
LITHIUM COMPOUNDS
LITHIUM HYDRIDES
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
ROTATIONAL STATES
SUDDEN APPROXIMATION