Close-coupling studies of rotationally inelastic HF--HF collisions at hyperthermal energies

Journal Article · Sat Nov 15 04:00:00 EST 1980 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.439992· OSTI ID:6878491

Alexander, M H

Earlier close-coupling studies on HF--HF system (A. E. DePristo and M. H. Alexander, J. Chem. Phys. 66, 1334 (1977)) have been extended to larger channel bases, allowing determination of converged integral cross sections for excitation out of the lower rotational levels of the bimolecular system. The calculations were confined to collision energies appropriate to supersonic beam experiments (E =0.5--1.5 eV). Two potential surfaces were used, both taken from our earlier fit to ab initio points (M. H. Alexander and A. E. DePristo, J. Chem. Phys. 65, 5009 (1976)). In the first surface symmetry of the only anisotropic term included corresponds to the standard dipole--dipole interaction; to which were added, in the second surface, a primarily repulsive anisotropy as well as the long-range dipole--quadrupole interaction. Largest cross sections (40--60 A/sup 2/) are associated with R--R processes of type j/sub 1/ j/sub 2/..-->..j/sub 1/ +- 1, j/sub 2/minus-or-plus1 which are dipole-allowed in first order. Magnitudes of these cross sections are little affected by presence of the shorter-range anisotropic terms, since much of the inelasticity occurs at large impact parameter. Cross sections for processes which are dipole-allowed only in second or higher order are considerably smaller (1--10 A/sup 2/), have classical dynamical thresholds at high energy, and are substantially lowered when the additional anisotropic terms are added to the potential, which has the effect of redirecting inelastic flux into the dipole forbidden channels. Cross sections for first order dipole--quadrupole transitions are also small, even in cases of near resonance. By contrast we find sizeable cross sections (7--15 A/sup 2/) for transitions which are coupled only by the short range anisotropy, which implies that rotational energy transfer between polar molecules cannot be fully described by models which rely solely on standard long-range multipole expansion of the potential.

• Research Organization: Department of Chemistry, University of Maryland, College Park, Maryland 20742
• OSTI ID: 6878491
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 73:10; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
COLLISIONS
ENERGY LEVELS
ENERGY TRANSFER
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXCITED STATES
HYDROFLUORIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
MOLECULE COLLISIONS
MOLECULE-MOLECULE COLLISIONS
ROTATIONAL STATES