A model for competitive binary and ternary ion–molecule reactions

A mechanism by which competitive binary and ternary ion–molecule reactions can occur is proposed. Calculations are undertaken for the specific system CH+3 +NH3+He which has been studied in the laboratory by Smith and Adams, and the potential surface of which has been studied theoretically by Nobes and Radom. It is shown that a potential energy barrier in the exit channel prevents the rapid dissociation of collision complexes with large amounts of angular momentum and thereby allows collisional stabilization of the complexes. The calculated ternary reaction rate coefficient is in good agreement with the experimental value but a plot of the effective two-body rate coefficient of the ternary channel vs helium density does not quite show the observed saturation.