Contributions of excitation autoionization to the electron-impact ionization ofMg+,Al2+, andSi3+in the distorted-wave approximation with exchange

Abstract

The contributions of excitation autoionization to electron-impact ionization in the Nalike ions ${\mathrm{Mg}}^{+}$, ${\mathrm{Al}}^{2+}$, and ${\mathrm{Si}}^{3+}$ are calculated using the distorted-wave approximation with exchange. Inner-shell excitations of the type $2p^{6}3s\to 2p^{5}3snl \mathrm{}(n=3,4;l=0,1,2\mathrm{})\mathrm{}$ are included. The calculations indicate that the largest contribution should be due to the $2p\to 3p$ excitations in all three elements, although the relative importance of this transition decreases with ionic charge. Comparisons of these results with recent experimental measurements indicate that the distorted-wave approximation overestimates the magnitude of the monopole-dominated $2p\to \mathrm{np}$ transitions. Possible reasons for this discrepancy between experiment and theory are discussed, and additional calculations and experiments are suggested.