Recent developments in dispersive kinetics

In general, chemical reactions proceeding on time scales comparable to, or shorter than, those of internal rearrangements in a reaction system renewin g the environment of the reactants (mixing), are dispersive. For dispersive kinetics, as for dispersive transport and dispersive relaxation, many time scales coexist. The rate coefficients for dispersive processes depend on t ime. For a time-dependent specific reaction rate, using the concept of ener gy profile along the reaction path, one finds the potential energy barrier separating reactants from products to evolve in time during the course of r eaction. The evolution of the energy barrier during the course of reaction is described in terms of energy distribution functions related directly to the distribution function of logarithms of lifetimes calculable from kineti c equations with a time-dependent specific reaction rate. This phenomenolog ical approach is compared with that in which the kinetic equations with tim e-dependent specific reaction rates are interpreted in terms of the superpo sition of classical reaction patterns. Special attention is paid to renorma lization of rate coefficients following from the stochastic theory of renew als (structural relaxation) in the reaction system. This phenomenological a pproach to kinetics is taken as a convenient basis to present a number of: comprehensive models of dispersive kinetics developed in the 1990s and to d iscuss some recently published experimental data to show what one derives d irectly from experimental data and what the detailed mechanistic models hav e to account for to be acceptable.