Cross sections for inner-shell excitation of Na-like ions

Abstract

The contributions of excitation autoionization to electron-impact ionization in the Nalike ${\mathrm{Al}}^{2+}$ and ${\mathrm{Si}}^{3+}$ are calculated using a two-state close-coupling approximation. Inner-shell excitations of the type $2p^{6}3s\to 2p^{5}3s3l\mathrm{}(l=0,1,2\mathrm{})\mathrm{}$ are included. The contributions of resonant-excitation double autoionization are estimated from a three-state close-coupling approximation with the aid of quantum-defect-theory analysis. These contributions explain the absence of the largest predicted excitation-autoionization step in the measurements of Crandall et al. Predictions for ${\mathrm{Mg}}^{+}$ also lead to similar agreement with experiment. We conclude that the experiments of Crandall et al. for the total ionization cross sections for ${\mathrm{Mg}}^{+}$, ${\mathrm{Al}}^{2+}$, and ${\mathrm{Si}}^{3+}$ by electron impact include measurements of the physical processes of direct-ionization, inner-shell excitation autoionization, and inner-shell resonant-excitation double autoionization.