Electron impact ionization of Ca+

The authors have carried out a number of close-coupling calculations for the electron impact excitation of the 3p53d4s configuration of Ca+ using the R-matrix method, so as to determine the indirect contribution to the ionization of Ca+. They find that the large resonance features primarily due to capture into the 3p53d24s configuration, present when only the 4P and the two 2P terms of the 3p53d4s configuration are included in the continuum close-coupling expansion, disappear when all nine terms of this configuration are included. The resulting ionization cross section is in reasonably good agreement with experiment over the energy range where dielectronic capture-autoionization features could be expected and resolves a long-standing disagreement between theory and experiment.