Gas‐Phase Elementary Chemical Reactions

Abstract Different levels of the field of chemical kinetics are related to each other by the following outline: Practical chemical systems Elementary chemical reactions Elementary chemical‐physical reactions Elementary physical reactions Time‐dependent quantum mechanics The theory of practical chemical kinetics is manipulation of rate constants of elementary chemical reactions by Bodenstein's steady‐state method. The experiments of elementary chemical reactions are the elements of the theory of practical chemical kinetics. The field of elementary chemical reactions has now become so mature that it is worthwhile to produce handbooks of data on the rate constants of elementary reactions in terms of appropriate macroscopic variables, k(T), k(T, M), or k(T, [M]). Complex rate phenomena can be understood in terms of the elementary steps, and new rate phenomena can be predicted from sets of elementary reactions. In this way tables of elementary rate constants and the theory of elementary chemical reactions can make an important contribution to other areas of chemistry, including chemical problems of the most practical sort. Theories of elementary chemical reactions are forced to make extensive (plausible) assumptions about potential‐energy functions, suitable coordinates, reaction cross sections, and molecular distribution functions. Direct experiments with molecular beams and new optical techniques are capable of giving actual observed data where the theory of elementary chemical reactions has traditionally been forced to make assumptions. Workers in these new fields need, perhaps, to be urged to keep a sympathetic eye on the “old‐fashioned” theories of elementary chemical reactions and to design some of the new experiments to confirm, or to deny, or to improve the postulates of these theories. The theory of elementary chemical‐physical and elementary physical reactions is fundamental, many‐particle quantum mechanics. Useful, approximate solutions for extremely simple systems can be carried out. For large atoms or molecules as reactants, there is considerable room for the development of effective new theoretical techniques in calculating elementary reaction rates. The field of chemical kinetics has a unity and a connectedness across its various levels of abstraction that should be understood and appreciated by all of its practitioners.