Theoretical calculations of the contributions of excitation autoionization to electron-impact ionization in ions of the transition series of elements

Abstract

Electron-impact excitation of inner-shell electrons followed by autoionization can dominate the total ionization cross sections in certain cases. We have made calculations to investigate this phenomenon for transitions of the form $n{p}^{6}n{d}^m\to n{p}^{5}n{d}^{m+1\mathrm{}}$ in ions of the transition series of elements. We predict such excitations lead to enhancements of the total cross section of more than an order of magnitude in the triply ionized species of Ti, Zr, and Hf in accord with recent crossed-beam experiments. In these cases, the predicted and measured positions and shapes of the resonances agree quite well; however, the magnitude of the theoretical cross sections is overestimated in the distorted-wave, dipole approximation used here. The effects of other kinds of excitation-autoionization transitions are considered, and trends along the first transition series are discussed.