Electron-impact ionization of Se2+

Absolute cross sections for electron-impact single and multiple ionization of Se 2+ ions were measured using the dynamic-crossed-beams technique over the energy range from the ionization threshold to 500 eV and compared to direct ionization cross sections predicted by the Lotz semi-empirical formula. The single-ionization cross section appears to be dominated by excitation-autoionization of the 4s and 3d inner subshells. The double-ionization measurements are reasonably well accounted for by the semi-empirical fitting formula of Shevelko et al that includes both direct double ionization of the outer 4p subshell and single ionization of the 3p and 3d subshells followed by autoionization. In addition to direct triple ionization, 3p and 3s ionization followed by double autoionization and excitation of the 3p and 3s subshells followed by triple autoionization likely contribute to the triple ionization cross section.