Microscopic Reversibility for Rates of Chemical Reactions Carried Out with Partial Resolution of the Product and Reactant States

Abstract

Applications of the principle of microscopic reversibility are considered for reaction rates measured in experiments that reveal some of the dependence on the rotational, vibrational, and/or translational states of the reactants or products. Each type of measurement establishes a characteristic set of quantum states for the reactants and products, suggesting that removal of trivial statistical factors (densities of states) from the data to retrieve a purely dynamical quantity ω̄(E), the state-to-state reaction rate suitably averaged over the initial and final sets of states at fixed total energy E. This quantity is fully symmetric with respect to the direction of the reaction—either the forward or reverse rate coefficient can be obtained by multiplying ω̄ with the proper density of final states. Thus ω̄ reflects the intrinsic probability of the process, disregarding the statistical bias introduced by the nature of the experiment itself. Methods of accurate computation of state densities appropriate to several kinds of detailed kinetic measurements currently feasible are given.