Selenium Valence-to-Core X-ray Emission Spectroscopy and Kβ HERFD X-ray Absorption Spectroscopy as Complementary Probes of Chemical and Electronic Structure

Selenium X-ray absorption spectroscopy (XAS) has found widespread use in investigations of Se-containing materials, geochemical processes, and biological active sites. In contrast to sulfur Kβ X-ray emission spectroscopy (XES), which has been found to contain electronic and structural information complementary to S XAS, Se Kβ XES remains comparatively under-explored. Herein, we present the first Se Valence-to-Core (VtC) XES studies of reduced Se-containing compounds and FeSe dimers. Se VtC XES is found to be sensitive to changes in covalent Se bonding interactions (Se–Se/Se–C/Se–H bonding) while relatively insensitive to changes in Fe oxidation states as selenide bridges in FeSe dimers ([Fe2Se2]2+ vs [Fe2Se2]+). Contrastingly, Se Kβ HERFD XAS is demonstrated to be quite sensitive to changes in Fe-oxidation state, with Se Kβ HERFD XAS demonstrating experimental resolution equivalent to K𝛼 HERFD XAS. Additionally, computational studies reveal both Se VtC XES and XAS to be sensitive to selenium protonation in FeSe complexes.