Ionization Produced by High-Energy Atomic Collisions

A statistical theory, developed earlier, to account for the ionization produced by violent collisions between two many-electron atoms is here re-examined in the light of recent experimental results. It is found that the statistical theory is consistent with the concept of an autoionization transition. This transition, which occurs after the collision is over, is between an initial state in the discrete spectrum of the atom and a final continuum state at the same energy. The statistical distributions introduced in the earlier papers are intimately related to the density of final states $\rho \left(E_f\right)$ in the standard formula for the transition probability between a discrete level and a continuum: $w=\left(\frac{2\pi }{\hslash }\right){\left|{H_{\mathrm{fi}}}^{\prime }\right|}^2\rho \left(E_f\right)$. In addition to reinterpreting the previous results, the statistical theory is here extended and improved, and simple algebraic expressions are obtained for the ionization probabilities. Finally, the ionization process is considered in detail, and a theory for the ionization energies appropriate to violent collisions is presented. It is shown that the appropriate ionization energies increase monotonically with the excitation energy of the autoionizing level and are always larger than the ionization energies as determined spectroscopically.