Semiclassical analysis of the anisotropic total cross section in thermal energy collisions between a non-spherical and a spherical atom

Thermal energy atomic collisions of the typeA(² P _3/2)+B(¹ S ₀) are discussed to clarify the dependence of the orientational anisotropy Δσ in the total cross section σ on the relative velocityv. Simple expressions for Δσ/σ are derived by semiclassical treatments designed to be appropriate for large spin-orbit interactions. The Δσ/σ oscillates withv around its average value. The velocities giving the extrema in the oscillating curve are almost solely determined by the isotropic part (bar Vleft( R right)) in the interaction potential, while the amplitude of the oscillation depends sensitively on the anisotropic interaction nearR _mi, whereR _mi is the location of the minimum in (bar Vleft( R right)) . The oscillation-averaged Δσ/σ is independent of the relative velocity and proportional to the anisotropy in the van der Waals interaction.