Semiclassical picture of collision-induced Λ-doublet transitions in diatomic molecules

Abstract

We investigate collision-induced Λ-doublet transitions in a system similar to NO+Ar, based on a semiclassical model in which nuclear motion is treated classically and electronic motion quantum mechanically. We present a picture of this process by monitoring 〈Λ〉, the expectation value of the projection of electronic orbital-angular momentum onto the molecular NO axis, over the duration of the collision. In a typical collision, the interaction with Ar would cause the electronic orbital-angular momentum to precess about the rotating NO–Ar vector. However, since this angular momentum is locked tightly to the diatomic axis, it is restricted to oscillation along this axis. This oscillation leads to transitions between Λ-doublet states. In addition to providing this physical picture of the collision process, we calculate an alignment effect of 1.2 for a hypothetical three-vector correlation experiment, neglecting spin.