Contributions of resonant excitation double auto-ionization to the electron-impact single-ionization cross-sections of Sn12+

Abstract

Electron-impact ionization cross-sections are key parameters for determining the ionization balance in hot dense plasmas. The total cross-sections of electron-impact single ionization (EISI) for the ground configuration $4s^{2}4p^{6}4d^2$ and the metastable state $4s^{2}4p^{6}4d4f$ of Sn¹²⁺ are theoretically investigated, which is important for optimizing extreme ultraviolet light sources. To calculate EISI cross-sections of complex atoms, a hybrid method is utilized, in which the ground and lowly excited configurations are considered by the fine-structure level approximation, and the highly excited configurations are treated by the relativistic configuration approach. The predominant contributions of the electron-impact single ionization cross-sections are attributed to direct ionization (DI) and excitation-auto-ionization (EA). The detailed resonant structures originating from resonant excitation double auto-ionization (REDA) are studied particularly. The present calculations are compared with the experimental results, which indicates that much better agreement can be achieved only when the contributions of REDA processes are taken into account.