INTERMOLECULAR ENERGY-TRANSFER PROBABILITIES FROM TRAJECTORY CALCULATIONS - A NEW APPROACH

A new method to calculate intermolecular energy transfer probability d ensity function P(E',E) from trajectory calculations is proposed. The method distinguishes between effective trajectories that contribute to P(E',E) and those with very large impact parameter which do not. The P(E',E) thus found obeys conservation of probability and detailed bala nce and is independent of the impact parameter. The method is demonstr ated for benzene-Ar collisions at various temperatures and internal en ergies. With this method it is possible to combine ab initio inter and intramolecular potentials with trajectory calculations, obtain P(E',E ) and use that in master equation calculations to obtain rate coeffici ents and populations distributions without resorting to any a priori a ssumptions and energy transfer models. In addition, the effects of int ernal energy, temperature and rotations on the average energy transfer red are discussed. Global potentials in center-of-mass and minimal dis tance coordinates which are obtained by averaging 20 000 and 50 000 tr ajectories are reported. It is shown that Lennard-Jones or ab initio p airwise potentials yield a Buckingham-type global potentials. (C) 1998 American Institute of Physics. [S0021-9606(98)02109-6].