Decay channels of core-excited HCl

Abstract

The HCl 2${\mathit{p}}_{\mathrm{Cl}}$→${\mathrm{\sigma }}^{\mathrm{*}}$ photoexcitation resonance has been studied using a tunable synchrotron radiation beam with a narrow bandwidth. Extensive ab initio molecular and atomic calculations have been carried out to analyze the details of the measured electron spectra. The interatomic potential-energy curves have been calculated for the ground and selected excited states of HCl using the complete-active-space self-consistent-field method. Multiconfiguration Dirac-Fock energies and line intensities of the atomic chlorine Auger spectrum have been used to identify the intense atomic spectral lines in the measured electron spectrum. Comparison between theory and experiment indicates fast neutral dissociation of the excited HCl molecules, followed by resonance Auger processes of the core-excited chlorine atoms. The atomic spectral lines are found to overlap with a strong background of broad structures, which sum up to 40% of the total intensity. This contribution has been addressed to the 2.9-eV potential well in our potential-energy curve of the excited HCl allowing for Franck-Condon transitions to bound vibrational states with a molecular nonradiative decay mode.