Correlation enhancement of the electron-impact ionization cross section for excited-state Ne-like ions

The electron-impact ionization cross section is calculated in the distorted-wave approximation for the Ne-like ions Ar⁸⁺, Ti¹²⁺, Fe¹⁶⁺, Zn²⁰⁺, and Se²⁴⁺. For ionization from the 2p⁶ ground state, the contributions from inner-shell excitation followed by autoionization are negligible. However, when these ions are initially in the 2p⁵3s excited configuration, contributions arising from the inner-shell excitations 2p⁵3s{→}2p⁴3snl and 2p⁵3s{→}2s2p⁵3snl are large. The overall branching ratio for autoionization of the 2p⁴3snl and 2s2p⁵3snl levels increases when the atomic-structure calculations are extended beyond the single-configuration approximation to include the configuration interaction. The resulting correlation enhancement of the excited-state ionization cross section is found to increase as a function of Z. For Se²⁴⁺ the correlation enhancement of the total ionization cross section is found to be 42%.