EFFECTS OF SUPERCOLLISIONS, ANALYTICAL EXPRESSIONS FOR COLLISION EFFICIENCY, AND AVERAGE ENERGY TRANSFERRED IN COLLISIONS

Supercollisions are collisions in which an inordinate amount of energy (e.g. more than 20 kcal/mol) is transferred in a single collision. Su percollisions were found by experimental and in trajectory calculation s and are discussed in the introduction of this paper. In the present work we have calculated values of the collisional efficiency beta by e xact solutions of a master equation and the values of the average ener gy transferred in all collisions (Delta E)(all) and in down collisions (Delta E)(d) with a supercollision double-exponential transition prob ability and by using the appropriate expressions for average quantitie s. Mixtures of 0.1% and 0.5% supercollision of 10 000 cm(-1) in weak c ollision of 300 cm(-1) were studied. Values of beta and (Delta E)(all) were also calculated by using modified known analytical expressions f or single-exponential transition probability functions where the (Delt a E)(d) quantity of a single exponential is replaced by the value of ( Delta E)(d) of a double exponential at the value of the average energy of the reacting molecules. A comparison between the exact and analyti cal values of beta and (Delta E)(all) shows that the deviations of the analytical from the exact values are small and the former can safely be used in the appropriate pressure and temperature ranges. Results ar e reported for cyclobutene isomerization to butadiene and cyclobutane fission to ethylene. It is shown that the value of the threshold energ y for reaction E(0) (32.2 kcal/mol for the former and 62.7 kcal/mol fo r the latter) plays a major role in defining the temperature range of the applicability of the analytical expression. In both cases studied, the analytical expression gave good results.