Ion-atom association reactions in the rare gases

A simple resonance theory of three-body ion-atom association reactions is presented. The reaction is considered as proceeding through the formation of a long lived orbiting resonance complex between the atom and the ion. The population of these quasibound states is estimated assuming thermal equilibrium. A stable molecular ion may then be formed upon deactivation of the complex by collision with a third body. Various simplifying approximations to the potential curves and surfaces are employed. For example, the orbiting complexes are determined by assuming that the long-range R -4 interaction, which is calculated from the atomic polarizabilities, is not important. Furthermore, the deactivation cross sections for the relevant complexes are estimated from the corresponding atomic 'sizes'. A simple analytical formula for the three-body rate constant is thus derived. Reasonable agreement with experiment is obtained for He + in He and fair agreement for other light systems.