THE CLASSICAL STATISTICAL-THEORY OF 3-ATOM REACTIONS GOVERNED BY SHORT-RANGE FORCES - ENERGY TRANSFERS AND RECOIL ENERGY-DISTRIBUTION

When the nascent products of a three atom reaction governed by chemica l forces separate, energy transfers may occur between vibrational, rot ational, and translational motions. In the first part of the paper, we show from quasiclassical trajectory calculations on a model potential energy surface that (a) the vibrational energy is adiabatic on averag e as usually assumed in statistical theories, (b) rotational-translati onal energy transfer mainly favors translational motion (as was initia lly suggested by Marcus), but that (c) this transfer is inefficient wh en the product atom is sufficiently light with respect to the other tw o. A qualitative analysis of these findings is proposed based on argum ents differing from those of Marcus, and Quack and Tree. In the second part of the paper, we extend the classical statistical formalism prop osed recently by ourselves, initially limited to reactions governed by long-range forces, to the present more general case of reactions invo lving tight transition states and for which energy transfers are ineff icient. In such a case, energy distributions at the exit transition st ate and in the products are the same. We focus our developments on the recoil energy distribution, Agreement between our theoretical result and the quasiclassical trajectory approach is shown to be very satisfa ctory. (C) 1995 American Institute of Physics.