Classical trajectory studies of energy transfer in Ar--difluorodiazirine collisions

We report the results of extensive classical trajectory studies of energy transfer in Ar--difluorodiazirine (DFD) collisions. The use of classical mechanics for this purpose leads to some difficulties of interpretation; these are discussed. In the conclusions drawn from the calculations, emphasis is placed on the qualitative results, and no attempt is made to estimate collision cross sections or transition probabilities. The most important results to emerge from our calculations are the following: (i) Classical mechanical simulations of Ar--DFD collisions lead to the conclusion that the induced mode-to-mode energy transfer is very selective, just as is observed. (ii) Despite thermal averaging, some idiosyncratic features of the potential energy surface are reflected in the average energy transfers due to collision (e.g., in the impact parameter dependence of the root-mean-square rotational energy change on collision). (iii) The branching pattern characteristic of collision induced mode-to-mode vibrational energy transfer is likely sensitive to details of the potential energy surface, and not just to its overall structure. We reach this conclusion because the particular pathways of collision induced mode-to-mode energy transfer in the Ar--1B1 DFD system are not correctly reproduced by our calculations, despite the correct prediction of selectivity in mode-to-mode energy transfer