Theoretical investigation of electron-impact multiple ionization of O ii-iv ions

Abstract

The electron-impact double ionization (DI) and triple ionization (TI) for O ii-iv ions are investigated using multistep approaches within the framework of many-body perturbation theory. The indirect DI and TI are treated as the single ionization of an inner-shell $1s$ electron followed by the single and double Auger decays, respectively. The knockout mechanism is employed to deal with the direct ionization process. The present approaches reproduce the available experimental cross sections for the DI of O ii-iv ions with much better accuracy compared to previous calculations. The TI cross sections of the O ii ion are calculated, which are in good agreement with the recent experimental data [Lecointre et al., J. Phys. B 46, 205201 (2013)]. It is found that the electron correlation effect and the energy distribution of the intermediate electron, which is taken as the incident electron of the subsequent knockout process, play an important role in the multistep treatment of the multiple ionization process.