The Activated Complex in Chemical Reactions

TLDR

Absolute reaction rates are calculated from available potential surface quantities, and the conditions for reducing the general statistical treatment to conventional kinetic theory are specified. The activated state probability is obtained via ordinary statistical mechanics and multiplied by the decomposition rate to yield the specific reaction rate. Quantized vibrations in the activated complex produce isotope reaction rates that differ markedly from those predicted by simple kinetic theory.

Abstract

The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the activated complex, in degrees of freedom which are unquantized in the original molecules, leads to relative reaction rates for isotopes quite different from the rates predicted using simple kinetic theory. The necessary conditions for the general statistical treatment to reduce to the usual kinetic treatment are given.