The contribution of the saddle point mechanism to the total ionization cross section in slow atomic collisions

Approximation analytic expressions for the total ionization cross section for H + -H and He 2+ -H collisions are obtained within the framework of the theory of non-adiabatic transitions in slow atomic collisions. Theoretical predictions for the cross section of the saddle point mechanism are presented. It is shown that this ionization channel contributes significantly to the total ionization. For both collision systems the calculated total ionization cross section agrees well with experimental data obtained by Shah et al. (1987).