Spin-orbit interaction and molecular-field effects in the L_2,3VV Auger-electron spectra of HCl

Ab initio calculations based on quantum chemical methods and the one center approximation have been carried out for the L_2,3VV 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_2,3MM 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^-1 states: 2p_3/2^-1(²Π_3/2), 2p_3/2^-1(²Σ_1/2⁺), and 2p_1/2^-1(²Π_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.