Theoretical investigation of electron-impact double ionization of B-like C+ to Ne5+ ions

Electron-impact double ionization (DI) including direct and indirect processes of B-like C+ to Ne5+ ions is investigated using a two-step approach. The direct process is treated as a primary single ionization (SI) and subsequent knockout mechanism. The indirect process is considered as a primary SI of an inner-shell 1s electron followed by a single autoionization. Based on the two-step approach, the DI cross sections are calculated using flexible atomic code with distorted-wave approximation. The potential of the intermediate ion is approximately equivalent to the mean potential constructed by three ions involved for calculating the cross section of the direct process, while using the potential of the ionizing ion in each step of the present two-step approach overestimates results. The present cross sections agree with available theoretical and experimental data.