Electronic Structure of Sulfur Studied by X-ray Absorption and Emission Spectroscopy

Abstract

An X-ray spectroscopy and theoretical study of the chemical state of several sulfur bearing minerals and a synthetic sodium sulfite sample was performed. X-ray absorption and high-resolution Kα X-ray emission spectra were recorded and compared to ab initio quantum chemical calculations. A consistent interpretation of the chemical shift in the Kα emission spectra is obtained based on three different theoretical approaches (density functional theory, multiple scattering theory, and atomic multiplet theory). An analysis of the theoretical sulfur orbital population and valence bond is in agreement with the fluorescence energy position of the Kα lines even within the sulfide (S2−) series. It is shown that the Kα energy shifts can be used for a quantitative determination of the proportion of different sulfur species in heterogeneous samples.

A compact dispersive refocusing Rowland circle X-ray emission spectrometer for laboratory, synchrotron, and XFEL applications

“…The extremely small pixels of the CMOS-based x-ray camera ensure negligible smearing to the spectrometer response function, e.g., ∆E/E ∼ 10 −5 or less. Comparing the S Kα spectral shape obtained here with that of Mori et al, 18 good agreement is seen after convolving their spectra with a 0.5 eV FWHM Gaussian profile. Given the reported resolution of 0.44 eV in the prior work, we find an experimental resolution of approximately 0.7 eV for the present instrument in the laboratory environment.…”

“…For both P Kα and S Kα emissions, the ALS measurements show slightly better resolution of the Kα 1,2 doublet but otherwise agree well with the laboratory results. Comparison of the ZnS S Kα signal taken at the ALS with results of Mori et al 18 as above finds a modest improvement in energy resolution compared to the laboratory, from approximately 0.7 to 0.6 eV.…”

“…valence electron population. 18 InP is chosen as a useful representative case not only because of its convenient chemistry in the present context but also because the surface of InP is readily oxidized, requiring rigorously air-free synthetic procedures for desired applications in solid-state lighting and biomedical imaging. 62,63 Hence, a bulk-sensitive quantification of the distribution of P oxidation states is of immediate relevance to characterizing and validating the synthesis process.…”

“…After an ensemble of internally consistent results is obtained, a single common energy shift is applied to all spectra so as to match, e.g., prior published results for one of the reference materials. 18,57 …”

“…More recent laboratory-based work in this energy range has seen an impressive extension to protoninduced x-ray emission analysis, 38,39 with the same Rowlandcircle instrument also seeing important use at a synchrotron endstation. 17,18,40 Here we present technical details and representative results for a dispersive x-ray emission spectrometer designed a) Author to whom correspondence should be addressed: seidler@uw.edu to function particularly well in this 2-2.5 keV energy range and demonstrate measurements on S and P XES both in the laboratory and at a synchrotron endstation. Our results include a representative, laboratory-based analytical application where we determine the distribution of oxidation states of P in InP quantum dots.…”