Vibrational energy transfer from four levels below 410 cm(-1) in S-1 p-difluorobenzene .2. A search for vibration to rotation transfer

Collision-induced vibrational energy transfer has been studied in S-1 p-difluorobenzene in a supersonic free jet expansion at similar to 30-40 K with the diatomic partners H-2, D-2, and N-2. Transfer has been studied from the initial levels 30(2) (E(vib)=240 cm(-1)), 8(2) (E(vib)=361 cm(-1)), 27(1) (E(vib)=403 cm(-1)) and 6(1) (E(vib)=410 cm(-)1)). The diatomic partners provide the possibility for transfer of vibrational motion in p-difluorobenzene to rotational motion in the diatomic (vibration to rotation transfer) in addition to the ubiquitous transfer of vibrational to translational motion. No compelling evidence is found for vibration to rotation transfer. Consequently, the diatomics are expected to behave analogously to monatomics, for which it has previously been observed that across the He to Kr series there is a substantial increase in multiple quanta (\Delta upsilon\>1) transfer. The results for the diatomics are qualitatively in accord with this trend, with increased multiple quanta transfer from H-2 to D-2 to N-2 However, the diatomics do not always slot into the monatomic series where expected. Furthermore, the particular channels observed to be prominent in the \Delta upsilon\=2 transfer for the diatomics are in a number of instances different to those seen for the monatomics. There are subtle but clear differences between these two classes of collision partner. The behavior of D-2 is particularly unusual, and at this stage unexplained. This collision partner has an unexpected preference for transfers involving multiple changes in vibrational quanta. The state-to-state branching ratios for transfer from 27(1) and 6(1) are very similar, suggesting that the initial vibrational motion and its symmetry play little role in determining the favored destination levels. (C) 1996 American Institute of Physics.