Alternative approach to light-induced drift in molecular gases

Ligh-induced drift of ethylene (${\mathrm{C}}_2$ ${\mathrm{H}}_4$) molecules upon rovibrational excitation is found to exhibit anomalous behavior as a function of the frequency detuning. This behavior, which shows a strong dependence on the rotational sublevels involved, has been investigated experimentally for ${\mathrm{C}}_2$ ${\mathrm{H}}_4$ immersed in Kr. For a qualitative explanation of these results a model is proposed that contains transport collision rates dependent not only on molecular vibration but also on molecular rotation.