Contributions of excitation autoionization to the electron-impact ionization of Mg+, Al2+, and Si3+ in the distorted-wave approximation with exchange

The contributions of excitation autoionization to electron-impact ionization in the Na-like ions Mg+, Al2+, and Si3+ are calculated using the distorted-wave approximation with exchange. Inner-shell excitations of the type 2p63s→2p53snl (n = 3,4; l = 0,1,2) are included. The calculations indicate that the largest contribution should be due to the 2p→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→np transitions. Possible reasons for this discrepancy between experiment and theory are discussed, and additional calculations and experiments are suggested