1. Theoretical. The theoretical approach

Abstract

There are a number of areas in chemical kinetics where generalizations have been helpful in interpreting and correlating a large body of experimental data in gas phase or solution reactions. I am reminded here of Bronsted’s relation between rate constants and equilibrium constants, Eyring’s and Evans and Polanyi’s work on transition state theory, Rice, Ramsperger and Kassel’s work on unimolecular reaction, later augmented to RRKM, treatments of the curve crossing problems, Hammett’s σρ relation and acidity function, and the subsequent equations they stimulated, theories of three-body recombination of atoms and of electron transfers in solution and at electrodes, simple BEBO calculations on activation energies, the Woodward-Hoffman rules and their implications for activation energies, Breit-Wigner and later treatments of resonances, models for ion-molecule reactions, to name a few. In the case of inelastic non-reactive collisions one would include the SSH theory, distorted wave theory for some systems, the Anderson theory of spectral line broadening and its later extensions. The interested observer, as well as the seasoned practitioner, might well ask which of these generalizations of analytical thought apply to current problems of molecular dynamics, what new ones have been developed, or what experimental generalizations are there, if any, which literally cry out for a theoretical answer. He might ask, too, whether the present field is sufficiently different from the previous ones that the approximate analytical theory will be literally swept under by a Spartan-like phalanx of exact classical trajectories and their semiclassical and quantum mechanical counterparts, with much analytical thought going into this army. We shall not attempt to answer all of these questions here, but shall summarize instead some of the trends which appear to be developing in the field. Calculations in the area are diverse, and some classification would be useful. A possible scheme for dynamical calculations is proposed in this introductory paper.