IX1. Significant Structures and Relaxations

Abstract

AbstractElementary reactions are controlled by a rate‐limiting step. This limiting step is ordinarily preceded and followed by faster steps. When the series of steps in a reaction sequence becomes comparable in speed, as is true for diffusion, the rate for the highest barrier alone must be divided by the total number of barriers n to give the overall rate. For a linearly rising envelope of the energy barriers, followed by a linear descent, n is the number of peaks within kT of the highest barrier. Fast reactions frequently involve a sequence of rate determining steps. For example viscosity, diffusion and electrical conductance in liquids are classic examples of very rapid processes. Non‐equilibrium, rate theory poses a fundamental question. Does the specific rate constant between two non‐degenerate quantum states at equilibrium apply to a non‐equilibrium population? Because the answer to this is “almost” we ordinarily assume complete forgetfulness of ancestry by the various segments of the populations making up a pure quantum state. To do otherwise makes life very hard but strict rigor requires such considerations for lines of finite width. Various examples of fast reaction rates are given.