Electron-impact ionization of the 4p⁶ subshell in strontium

Abstract

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 4p5nln′l′ states. The measurements were carried out in the energy range of incident electrons from the 4p6 ionization threshold at 26.92 eV 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 10-14 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)×10−18cm2 at 52 eV for the (4p54d5s)4P5/2 state and (3.0±0.5)×10−17cm2 at 112 eV for the (4p55s2)2P3/2 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)×10−17cm2 at 92 eV.

Excitation Dynamics of the 5p^6 Auger Spectra in Ba + e^– Collisions

“…There is also no contribution from the two-step autoionization for the lowest-lying quartet states 5p 5 5d 2 ( 3 F) 4 D 3/2 (line 2) and 5p 5 5d( 3 P)6s 4 P 3/2 (line 4). Interestingly, a similar observation was previously made, when studying the ionization of the 4p 6 shell in Sr atoms [13].…”

“…The assignment of lines and energies of the corresponding ionic states are presented in Table . Two shapes of the cross-sections are observed with maxima at low and high impact energies. As was shown by analyzing the excitation dynamics of the 4p 5 𝑛𝑙𝑛 ′ 𝑙 ′ states in Sr + [13], the first type of cross-sections should reflect the formation of states with a dominant quartet character. However, in our data, this conclusion is consistent only with identifying lines 2 and 4 as the 5p 5 5d 2 ( 3 F) 4 D 3/2 and 5p 5 5d( 3 P)6s 4 P 3/2 quartet states.…”