Electron-impact ionization of atomic ions in the Na isoelectronic sequence

Abstract

Electron-impact ionization cross-sections and rate coefficients for the Na-like ions Mg+, Ar7+, Kr25+, Sn39+, Xe43+ and W63+ are presented. The direct ionization cross-sections of 2s, 2p and 3s subshells are calculated within a configuration-average distorted-wave (CADW) method. In addition, excitation–autoionization contributions originating from the inner-shell excitations of the type 2s22p63s→2s22p53snl (n=3–6) and 2s22p63s→2s2p63snl (n=3–6) are calculated using both CADW and level-resolved distorted-wave (LLDW) methods. We include the branching ratios for the radiation damping of the autoionizing configurations and levels. The excitation–autoionization contributions are found to be quite large for the lighter ions. For the heavier ions the radiation damping of the excitation–autoionization contribution is found to be significant. We find that the distorted-wave results are in good agreement with available experimental measurements, which only exist for Mg+, Ar7+ and Xe43+. We also find that the computationally simple configuration-average calculations are in reasonable agreement with the computationally demanding level-resolved calculations for the excitation–autoionization contributions for all the Na-like ions studied. In addition, Maxwellian rate coefficients are produced from our cross-sections and are archived in a format useful for plasma modelers.