Distorted-wave electron-impact ionization cross sections for the argon isoelectronic sequence

Electron-impact ionization cross sections have been calculated in a distorted-wave exchange approximation for seven ions in the argon isoelectronic sequence. For neutral argon, target configuration interaction and term dependence in the ejected-electron continuum were found to be significant influences on the cross section. Similarities of electron ionization and photoionization are discussed. An analytic fit is given which accurately reproduces the distorted-wave cross sections and rate coefficients of argonlike ions with $Z\ge 20$.