DIRECT AND CORRECT CALCULATION OF CANONICAL AND MICROCANONICAL RATE CONSTANTS FOR CHEMICAL-REACTIONS

Theoretical approaches for calculating rate constants of chemical reac tions-either the microcanonical rate for a given total energy k(E) or the canonical rate for a given temperature k(T)-are described that are both ''direct'', i.e., bypass the necessity of having to solve the co mplete state-to-state quantum reactive scattering problem, yet also '' correct'', i.e., in principle exact (given a potential energy surface, assuming nonrelativistic quantum mechanics, etc.) Applications to a v ariety of reactions are presented to illustrate the methodology for va rious dynamical situations, e.g., transition-state-theory-like dynamic s where the system moves directly through the interaction (transition- state) region and reactions that form long-lived collision complexes. It is also shown how this rigorous quantum theory can be combined with the Lindemann mechanism for describing the effects of collisions with a bath gas, so as to be able to treat recombination reactions and oth er effects of pressure. Finally, several ways are discussed for combin ing these rigorous approaches for small molecule dynamics with an appr oximate treatment of (perhaps many) other degrees of freedom (i.e., a solvent, a substrate, a cluster environment) that may be coupled to it .