SOME NEW ASPECTS OF PRODUCT DISTRIBUTION-FUNCTIONS FOR 3-ATOM UNIMOLECULAR REACTIONS PERFORMED IN-BEAM EXPERIMENTS

Energy distribution functions for the products in two classes of three -atom unimolecular reactions performed in beam experiments are derived which are much more realistic than the prior distribution functions ( PDF) of Levine and Bernstein without being more complicated, In a firs t step, we deal with light-atom emission processes governed by short-r ange forces. Contrary to what is generally believed, we emphasize the applicability of statistical theory of energy distributions to such re actions in which the change in energy partitioning from critical confi guration to products is weak If not negligible. In a second step, we t reat within the framework of phase space theory (PST) this more usual case of processes governed by long-range farces for which, however, th ere exists no realistic distribution functions. Comparison with experi mental results or with results of simulations and/or results obtained using PDF, PST, or the statistical adiabatic channel model (SACM) is d one for the following processes: (i) C2H --> C-2 + H (model alkyl diss ociation reaction), (ii) O3H --> O-2 + H, (iii) NO2 --> NO + O, and (i v) Al-3 --> Al-2 + Al. For reaction i which proceeds through a barrier and for reaction ii which is barrierless but involves strong angular anisotropies in the exit-channel part of the potential energy surface, the distributions derived by our method are much more realistic than those obtained using BST or SACM.