Electron-impact ionization of Fe8+

Abstract

Electron-impact ionization cross sections and Maxwellian rate coefficients are presented for the Fe8+ion by considering processes from the ground and metastable levels. The lifetimes of the levels for the 3s23p53d configuration were analysed using the extended basis of interacting configurations. Convergence of the cross sections for the indirect process due to excitations to the high-nlsubshells was investigated. We demonstrate that excitations to the subshells with orbital quantum numberl = 3 with subsequent autoionization dominate up to electron energies of ∼700 eV for the ground and metastable levels. Modelling of theoretical cross sections obtained for the ground and metastable levels to produce the best fit to the measurements shows that 15% of ions reach the reaction zone in the metastable state. The obtained results contradict the previous work that showed ∼30% for the metastable fraction.