Trajectory studies on the collisional relaxation of highly excited benzenes by mono- and polyatomic colliders

Collisional energy transfer (GET) of highly vibrationally excited benzene and hexafluorobenzene molecules has been investigated by quasiclassical trajectory calculations. Influences of the intramolecular potential reflected in molecular parameters are studied systematically in collisions with argon. It is found that the lower the vibrational frequencies the more efficient is GET. Intermolecular potential effects are investigated. At larger well depths (for benzene + argon) the first moment of energy transfer (Delta E) scales with epsilon and is not very sensitive to details of the interaction. However at small well depths epsilon (for benzene + helium) energy transfer is dominated by the exact shape of the intermolecular potential, especially of the repulsive part. Benzene-benzene collisions are studied as an example for CET between polyatomics and large colliders. Excellent quantitative agreement with experiment is found for (Delta E) and its energy dependence. The results suggest that vibrational energy loss of the excited molecule is dominated by V-V transfer and that the rotation is heated up more strongly with increasing epsilon, an effect also present for noble gas colliders.