Three-body Ionic Recombination

Abstract

THOMSON'S theory¹ of three-body recombination of positive and negative ions: invokes the artifice of a fictitious trapping distance such that recombination may be supposed to occur if either ion collides with a neutral molecule when within this distance from the other. In recent years the theory has been elaborated by several investigators² and the predictions regarding the recombination coefficient have consequently been considerably modified. However, the basic artifice is retained though it does not form an altogether satisfactory foundation on which to build a precise theory. We here outline an entirely different approach exploiting the fact that a quasi-equilibrium is quickly established in which the rate at which bound ion-pairs are formed and destroyed is very much greater than the rate at which their number density changes³. In so far as the contribution from charge transfer is merely additive, our approach is effectively exact in the region where the three-body recombination coefficient α is directly proportional to the number density, N(M), of neutral atoms.