Adiabatic long-range rotationally inelastic collisions in Li*2(A 1Σ)–Xe: Experiment and theory

Abstract

A recent study of the velocity dependence of rotationally inelastic (RI) collision cross sections in Li*2 –rare gas systems has shown the Δ≡jf−ji=±2 cross sections in Li*2–Xe to be exceptional in their large size and rising velocity dependence. A simple semiclassical time dependent perturbation treatment using the long-range R−6 dispersion potential will be shown to provide an excellent description of the magnitude and velocity dependence of these cross sections. The analysis explicitly accounts for the molecular rotation during the collision, which is shown to cause the substantial adiabatic reduction of these ‖Δ‖=2 cross sections at lower velocity. The observation that almost all other RI collision cross sections in Li*2–rare gas systems decrease with larger velocity suggests that long-range collisional contributions and rotationally adiabatic effects are not of general importance for these collisions. New experimental as well as theoretical investigations into vib-rotationally inelastic collisions in Li*2–Xe suggest that vibrational inelasticity may have been previously mistaken for rotational adiabaticity when accounting for the general decrease in RI cross sections at larger ji.