Speciation of iron sulfide compounds by means of X-ray emission spectroscopy using a compact full-cylinder von Hamos spectrometer

Abstract

We present experimental and theoretical X-ray emission spectroscopy (XES) data of the Fe Kβ line for iron(II)sulfide (FeS) and iron(II)disulfide (FeS₂). In comparison to X-ray absorption spectroscopy (XAS), XES offers different discrimination capabilities for chemical speciation, depending on the valence states of the compounds probed and, more importantly in view of a broader, laboratory-based use, greater flexibility with respect to the excitation source used. The experimental Fe Kβ XES data were recorded using polychromatic X-ray radiation and a compact full-cylinder von Hamos spectrometer while the calculations were realized using the OCEAN code. The von Hamos spectrometer used is characterized by an energy window of up to 700 eV and a spectral resolving power of E/ΔE = 800. The large energy window coverey by the spectrometer components is beneficial to circumvent the instrumental sensitivity of wavelength-dispersive spectrometers to sample positioning. This results in a robust energy scale which is used to compare experimental data with ab initio valence-to-core calculations, which are carried out using the OCEAN package. To validate the reliability of the OCEAN package for the two sample systems, near edge X-ray absorption fine structure measurements of the Fe K absorption edge are compared to theory using the same input parameters as in the case of the X-ray emission calculations. Based on the example of iron sulfide compounds, the combination of XES experiments and OCEAN calculations allows unravelling the electronic structure of different transition metal sulfides and qualifying XES investigations for the speciation of different compounds.