Excitation-autoionization contribution to single ionization of Sr by electron impact

Abstract

The 4p6 excitation-autoionization (EA) cross-section of Sr atoms has been measured at electron-impact energies from the threshold to 600 eV. The cross-section has a pronounced resonance character in the near-threshold region, reaching its maximum value of (2.5 ± 0.8) × 10−16 cm2 at 24.5 eV. The shape and absolute value of the cross-section are determined by the excitation dynamics and the decay mode of autoionizing states from 4p54d5s2, 4p54d2nl and 4p54d5snl configurations. A comparative analysis of the measured EA cross-section, the calculated 5s2 ionization cross-section and the available ionization data showed that (i) direct ionization of the 5s2 shell and EA of the 4p6 shell adequately describe the single ionization of Sr atoms; (ii) 4p6 EA contribution reaches 25% of the total single ionization cross-section of Sr atoms.