Spin-orbit interaction and molecular-field effects in theL2,3VVAuger-electron spectra of HCl

Abstract

Ab initio calculations based on quantum chemical methods and the one center approximation have been carried out for the ${L}_{2,3}\mathrm{VV}$ normal Auger-electron spectrum of HCl. Spin-orbit and molecular field effects were explicitly included in the description of the intermediate $2p$ core hole state. The results are compared with the experimental spectrum obtained with synchrotron radiation. The corresponding atomic ${L}_{2,3}\mathrm{MM}$ Auger transitions are studied in the isoelectronic argon atom. The calculated Auger electron spectra are in good agreement with the experimental and to previous theoretical results. For HCl the calculations predict substantially different total Auger transition probabilities of 126, 99, and 113 meV for the three nondegenerate spin-orbit and molecular-field-split ${2p}^{\ensuremath{-}1}$ states: ${2p}_{3/2}^{\ensuremath{-}1}{(}^{2}{\ensuremath{\Pi}}_{3/2}),$ ${2p}_{3/2}^{\ensuremath{-}1}{(}^{2}{\ensuremath{\Sigma}}_{1/2}^{+}),$ and ${2p}_{1/2}^{\ensuremath{-}1}{(}^{2}{\ensuremath{\Pi}}_{1/2}),$ respectively. Furthermore, each of these core hole states gives rise to remarkably different intensity distributions. These effects are explained by (i) the partial orientation of the chlorine $2p$ core hole by the molecular field, (ii) a decrease of the net population of the chlorine $3p$ orbital in the bond direction due to the chemical bond, and (iii) the clear (97%) preference of the Auger decay of an oriented $2p$ core orbital to produce final states with at least one hole in the $3p$ orbital with the same spatial orientation.