Electron-impact ionization of atomic ions in the W isonuclear sequence

Abstract

Electron-impact ionization cross sections for all atomic ions in the W isonuclear sequence are calculated using a variety of theoretical methods. For the direct ionization process, a semirelativistic configuration-average distorted-wave method is used for low to moderately charged ions, while a fully relativistic subconfiguration-average distorted-wave method is used for highly charged ions. For the indirect ionization process of excitation autoionization, a semirelativistic configuration-average distorted-wave method is used for the bulk of the transitions, but a semirelativistic level-resolved distorted-wave method is used for selective strong transitions that may straddle the ionization threshold. For moderately charged ions it is important to include radiation damping of the excitation-autoionization process through explicit calculation of autoionization branching ratios. Checks are made on the theoretical predictions by comparison with available crossed-beams experimental measurements, which only exist for low stages of ionization. The ionization cross sections for the entire W isonuclear sequence are converted to temperature-dependent rate coefficients and put in a collisional-radiative format that should prove useful in modeling laboratory plasmas that contain W impurities.