DYNAMICS OF RARE-GAS ATOM DIATOM REACTIONS

Quasiclassical trajectory calculations have been carried out for reactions between rare-gas atom-diatom pairs of Kr + Ar2, Xe + Ar2, and Kr + Xe2. A potential energy surface represented by pairwise additive diatomic Morse potentials plus a three-body Axilrod-Teller term was used. Experimental scattering angle distributions and the form of the excitation function (is-proportional-to E-1.9) were nearly reproduced. A detailed analysis of time-dependent trajectories indicates that most reactive encounters involve either a knock-out or a sequential impulse collision, with virtually no stripping mechanism in action over the entire collision energy range studied. The branching ratio of knock-out vs sequential impulse collisions increases as the kinematics change from heavy-light-light (Xe + Ar2) to light-heavy-heavy (Kr + Xe2) case. For given kinematics, branching between the two channels depends critically upon the vibrational phase at the time of impact: contracting diatoms lead to sequential impulse collisions, while expanding diatoms favor knock-outs. In contrast to the case of bulk properties, there was virtually no effect of the three-body triple-dipole interaction on the overall reaction dynamics.