Quasistatistical Complexes in Chemical Reactions

Abstract

The S matrix for inelastic and rearrangement collisions derived within Feshbach's theory of resonances can be written as the sum of SD and SC, where SD refers to direct interaction processes, and SC refers to complex (resonant) processes. For collision times short compared to characteristic times of internal motions of reactants, models of direct interactions, which assume SC to be zero, have been developed. For collision times long compared to all characteristic times of internal motion, statistical models of complex formation, which assume SD to be zero, have been formulated. Although much experimental work can be classified with either of these extreme models, intermediate cases do occur. We examine a possible method for making quasistatistical (or partial statistical) approximations on SC (for inelastic and reactive scattering), and indicate how well-known statistical models can be modified with this method to describe quasistatistical behavior. The concept of doorway states provides another category of intermediate cases and is developed briefly. The classification of experimental results into the various categories (direct interaction, complete statistical complex, partial statistical complex, doorway states, and combinations of all of these) requires a number of different measurements. Possible deductions from the various experiments are discussed and examples of reactions for the different categories are cited.