Satellite-Dominated Sulfur L2,3 X-ray Emission of Alkaline Earth Metal Sulfides

The sulfur L2,3 X-ray emission spectra of the alkaline earth metal sulfides BeS, MgS, CaS, SrS, and BaS are investigated and compared with spectra calculations based on density functional theory. Very distinct spectral shapes are found for the different compounds. With decreasing electronegativity of the cation, that is, increasing ionic bonding character, the upper valence band width and its relative spectral intensity decrease. These general trends are qualitatively reproduced by the spectra calculations, which give quite an accurate description of the spectral shapes in the upper valence band region. On the low energy side of the sulfur 3s-* 2p transition dominating the spectra, we find strong satellites caused by semi-Auger decays involving configuration interaction. These satellites, previously believed to be energetically forbidden for sulfur L2,3 emission and only observed for the L2,3 emission of Cl to Cr, increase in intensity as the bonding character becomes more ionic and dominate the spectra for SrS and BaS. The intensities, energies, and widths of the satellites vary strongly between the investigated compounds, giving a very specific spectral fingerprint that can be used for speciation analysis.

Automated summary

The sulfur L2,3 X-ray emission spectra of alkaline earth metal sulfides have been investigated. The results show distinct spectral shapes for different compounds, and the spectral calculations based on density functional theory provide an accurate description of the spectral shapes in the upper valence band region. Semi-Auger decays involving configuration interaction produce strong satellites on the low energy side of sulfur 3s-*2p transition, which become more intense as the bonding character becomes more ionic. These satellites can be used as a specific spectral fingerprint for speciation analysis.