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

The contributions of excitation autoionization to electron-impact ionization in the Nalike Al²⁺ and Si³⁺ are calculated using a two-state close-coupling approximation. Inner-shell excitations of the type 2p⁶3s→2p⁵3s3l(l=0,1,2) 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 Mg⁺ also lead to similar agreement with experiment. We conclude that the experiments of Crandall et al. for the total ionization cross sections for Mg⁺, Al²⁺, and Si³⁺ by electron impact include measurements of the physical processes of direct-ionization, inner-shell excitation autoionization, and inner-shell resonant-excitation double autoionization.