Electron-impact ionization of the 4p6 subshell in strontium

Electron-impact ionization of the 4p6 subshell in Sr atoms has been studied by observing the excitation dynamics of the electron spectra arising from the Auger decay of the 4p 5nln′l′ states. The measurements were carried out in the energy range of incident electrons from the 4p6 ionization threshold at 26.92 to 600 eV. At near-threshold impact energies, the effect of post-collision interaction was found for most of the Auger lines. The identification of 21 lines observed between 10 and 14 eV electron energy showed that the 4p6 Auger spectrum of Sr atoms is completely described by the configurations 4p54d5s, 4p55s2 and 4p54d2. The cross sections for the lowest quartet and doublet states in 4p54d5s and 4p55s2 configurations have been obtained with the maximum values of ( 3.5±0.5)×10−18 cm2 at 52 eV for the (4p54d5s)4P 5/2 state and ( 3.0±0.5)×10−17 cm2 at 112 eV for the (4p55s2)2P 3/2 state. Configuration interaction and excitation-autoionization processes determine the energy behavior of the excitation cross sections of doublet states. The lower limit of the total ionization cross section of the 4p6 subshell in Sr has been obtained with the maximum value of ( 6.2±1.2)×10−17 cm2 at 92 eV.