Three-body recombination of positive and negative ions II. General third body

A quasi-equilibrium statistical theory is used to investigate the low density limit to the rate of the three body ionic recombination process X$^+$+Y$^-$+Z$\rightarrow$[XY]+Z, the interaction between the third body and an ion being taken to be of the Langevin form. It is shown that the recombination coefficient $\alpha$ is, to a close approximation, equal to the sum of two partial recombination coefficients, $\alpha_{13}$ and $\alpha_{23}$ the former describing recombination due only to X$^+$ - Z collisions and the latter describing recombination due only to Y$^-$ - Z collisions. Results are presented which enable $\alpha$ to be found for a wide range of values of the temperature, the masses of the three species involved, the two Langevin hard-sphere radii and the polarizability of the third body. In the case of equal masses (for which it was designed) the well-known theory of Thomson is remarkably successful with regard to its predictions on the dependence of $\alpha$ on the temperature and on the interactions.