Description of light-induced drift in terms of transport mean paths

Abstract

Light-induced drift is often described in terms of a change Delta nu in the collision rate (or of the transport collision rate) caused by optical excitation of atoms or molecules immersed in a buffer gas. One assumes (at least tacitly) that the collision rates are independent of velocity, though this is true only for heavy particles in a light buffer gas. The recently observed anomalous light-induced drift of molecular gases suggests using a speed-dependent Delta nu which, however, is difficult to justify. The formulation in terms of speed-dependent transport mean paths, proposed here, is free of such ambiguities. For molecules a Wang-Chang-Uhlenbeck-de Boer multilevel formalism leads to extended transport mean paths, whereupon anomalous light-induced drift can be interpreted in a plausible way.