DESCRIPTION OF LIGHT-INDUCED DRIFT IN TERMS OF TRANSPORT MEAN PATHS

Light-induced drift is often described in terms of a change DELTAnu in the collision rate (or of the transport collision rate) caused by opt ical excitation of atoms or molecules immersed in a buffer gas. One as sumes (at least tacitly) that the collision rates are independent of v elocity, though this is true only for heavy particles in a light buffe r gas. The recently observed anomalous light-induced drift of molecula r gases suggests using a speed-dependent DELTAnu which, however, is di fficult to justify. The formulation in terms of speed-dependent transp ort mean paths, proposed here, is free of such ambiguities. For molecu les a Wang-Chang-Uhlenbeck-de Boer multilevel formalism leads to exten ded transport mean paths, whereupon anomalous light-induced drift can be interpreted in a plausible way.