Multielectron ionization contributions in valence-to-core x-ray emission spectra of third-row elements

The valence-to-core (VtC) K x-ray emission spectroscopy (XES) in the tender x-ray range is emerging as a powerful analytical technique used to study the electronic structure of third-row elements within complex bulk materials. With dedicated tender x-ray emission spectrometer coupled with laboratory excitation source, such analysis can be successfully performed also in a smaller lab. In this work, we have gathered VtC x-ray emission spectra of several sulfur and chlorine compounds measured previously in our home lab using Johansson type tender x-ray emission spectrometer and MeV proton excitation. Measured spectra are compared to the results of one-electron density functional theory (DFT) calculations. Theoretical spectra were found in good agreement with the experimental data with few exceptions where systematic discrepancies were observed. The latter was attributed to the simultaneous K and M shell ionization induced by MeV protons, which is not included in the one-electron DFT theoretical framework. In order to confirm this also experimentally, VtC x-ray emission spectra of few selected S and Cl compounds induced with three different proton energies were recorded yielding characteristic KM ionization satellite lines, confirmed by their emission energies as well as the dependence of their relative intensity on proton energy.