The energy structure and decay channels of the 4p6-shell excited states in Sr

Abstract

The ejected-electron spectra arising from the decay of the 4p autoionizing states in Sr atoms have been studied precisely at the incident-electron energies close to excitation and ionization thresholds of the subshell. The excitation behaviors for 58 lines observed between 12 and 21 eV ejected-electron kinetic energy have been investigated. Also, the ab initio calculations of excitation energies, autoionization probabilities and electron-impact excitation cross sections of the states 4p (nl = 4d, 5s, 5p; = 4d, 5s, 5p; = 5s, 6s, 7s, 8s, 9s, 5p, 6p, 5d, 6d, 7d, 8d, 4f, 5g) have been performed by employing the large-scale configuration-interaction method in the basis of the solutions of Dirac–Fock–Slater equations. The obtained experimental and theoretical data have been used for the accurate identification of the 60 lines in ejected-electron spectra and the 68 lines observed earlier in photoabsorption spectra. The excitation and decay processes for 105 classified states in the 4p55s, 4p54d and 4p55s configurations have been considered in detail. In particular, most of the states lying below the ionization threshold of the 4p6 subshell at 26.92 eV possess up to four decay channels with formation of Sr+ in 5s, 4d and 5p states. Two-step autoionization and two-electron Auger transitions with formation of Sr2+ in the 4p6 ground state are the main decay paths for high-lying autoionizing states. The excitation threshold of the subshell in Sr has been established at 20.98 ± 0.05 eV.