Abstract
Recent identifications of autoionizing thresholds in the cross section for electron impact excitation of the ground state of Ba II as being due to levels in the p5ds configuration have been extended to Ca II and Sr II. A new result is that the most prominent threshold is due to exchange. The energy calculations are improved by taking the p5ds from or to p5l2 interactions (l=s, p' and d) into account. For the 2P terms, the influence of these interactions is found to be fairly small. The exception is Mg II for which the interacting configurations belong to the same complex. The importance of this result for the analysis of inner-shell absorption spectra in the Na I isoelectronic sequence is pointed out.

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