INFLUENCE OF MOLECULAR ROTATION ON LIGHT-INDUCED DRIFT OF CH3F

Experimental results on light-induced drift of (ro)vibrationally excited CH3F immersed in the noble buffer ps Kr or in the polar buffer gas CH3Cl are presented. For pure vibrational excitation, the relative change in collision rate is found to be essentially velocity independent. For rovibrational excitation, this quantity can have a significant velocity dependence, as can be concluded from the detuning behaviour of light-induced drift for two transitions of CH3F immersed in Kr. In combination with earlier observations of anomalous light-induced drift in C2H4, these results demonstrate that a sizable velocity dependence of the change in collision rate caused by rovibrational excitation is a general feature for molecular systems. Additionally, while the transport collision rate generally increases with vibrational quantum number, the data suggest that it decreases with increasing rotational quantum number. Finally, the data for CH3F in CH3Cl indicate that rotational-state-changing collisions are accompanied by a significant velocity change.