Electron-impact ionization and recombination of M -shell atomic ions in the argon isonuclear sequence

Abstract

Electron-impact ionization and recombination cross sections and rate coefficients are calculated for M -shell Ar atomic ions using a configuration-average distorted-wave method. The electron-impact ionization calculations are for all atomic ions in the Ar isonuclear sequence. Ionization contributions include both direct ionization and excitation-autoionization processes. Good agreement is found between theory and experimental crossed-beam measurements for moderately charged ion stages. Comparisons are made with previous theoretical calculations where possible. We also generate rate coefficients for neutral argon ionization, based on recent R -matrix with pseudostates calculations. Electron-impact dielectronic recombination is calculated for all M -shell ions of argon. For Ar6+ and Ar7+ the current theoretical results agree well with previous level-resolved distorted-wave calculations. In order to compare with published ionization balance results our dielectronic recombination data are combined with literature values for the higher ion stages and with recent radiative recombination data for all the ion stages. We find significant differences in our equilibrium fractional abundances for the M -shell ions, compared with literature values. We relate these differences to the underlying atomic data. © 2007 The American Physical Society.