MOLECULAR AND PHENOMENOLOGICAL RATE COEFFICIENTS OF FAST REACTIONS INSOLUTIONS

The paper is concerned with the problem of formulating chemical rate e quations for reversible reactions in solution in terms of concentratio n-independent, phenomenologic rate coefficients. These time-dependent rate coefficients approach after an initial transient, the rate consta nts that can be obtained in a relaxation experiment. We start with the coupled evolution equations for the macroscopic concentrations, and f or the two-particle distribution functions describing association-diss ociation (A + B reversible arrow C), bimolecular isomerization (A + B reversible arrow B + C), and double decomposition (A + B reversible ar row C + D). The effects of interparticle forces and long-ranged reacti vity are included. We derive general identities linking the reactants and products radial distribution functions. For association-dissociati on this leads to relations among the molecular rate coefficients which are valid for both contact and long ranged reactivities. For the othe r two reaction types, we were able to derive analogous relations only for contact reactivities. We demonstrate how the phenomenological rate coefficients can be defined via the solutions of the corresponding di ffusional boundary-value problems. This approach is quite general, and valid for both contact and long-ranged reactivities and if interactio n forces are included. (C) 1995 American Institute of Physics.