Close-coupling studies of the orientation dependence of rotationally inelastic collisions

Abstract

Orientation effects in rotationally‐inelastic Ar–N₂ collisions are investigated using a quantum close‐coupling description of the collision dynamics to obtain differential and integral m_j‐dependent cross sections for the j=0→2,4,6 and j=2→4,6 transitions. For a model potential surface which contains a substantial degree of long‐range anisotropy, the inelastically scattered products are significantly polarized with respect to a quantization axis perpendicular to the scattering plane. With respect to the initial relative velocity vector, the products are preferentially aligned in the m_j=0 state, in agreement with earlier predictions based on the l‐dominant limit. The m_j‐dependence of the integral cross sections corresponding to an initially unpolarized beam can be well fit by a Gaussian distribution when the anisotropy is long‐ranged, but are essentially statistical when the anisotropy is primarily repulsive in nature. Independent of the nature of the anisotropy, the classical alignment angle appears to be conserved during inelastic collisions.