PNNL

Abstract

An extensive experimental and theoretical study of the Ka and Kß high-resolution x-ray emission spectroscopy (XES) of sulfur-bearing systems is presented. This study encompasses a wide range of organic and inorganic compounds, including numerous experimental spectra from both prior published work and new measurements. Employing a linear-response time-dependent density functional theory (LR-TDDFT) approach, strong quantitative agreement is found in the calculation of energy shifts of the core-to-core Ka as well as the full range of spectral features in the valence-to-core Kß spectrum. The ability to accurately calculate the sulfur Ka energy shift supports the use of sulfur Ka XES as a bulk-sensitive tool for assessing sulfur speciation. Fine structure of the sulfur Kß spectrum, in conjunction with the theoretical results, is shown to be sensitive to the local electronic structure including effects of symmetry, ligand type and number, and, in the case of organosulfur compounds, to the nature of the bonded organic moiety. This agreement between theory and experiment, augmented by the potential for high-access XES measurements with the latest generation of laboratory-based spectrometers, demonstrates the possibility of broad analytical use of XES for sulfur and nearby third-row elements. The effective solution of the forward problem, i.e., successful prediction of detailed spectra from known molecular structure, also suggests future use of supervised machine learning approaches to experimental inference, as has seen recent interest for interpretation of x-ray absorption near edge structure (XANES). This research and was partially supported by the National Science Foundation (NSF) through the UW Molecular Engineering Materials Center, a Materials Research Science and Engineering Center (DMR-1719797). EPJ was supported in part by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, and Basic Energy Sciences. EPJ was also supported in part by a subcontract from the National Institute of Standards and Technology. Opinions, recommendations, findings, and conclusions presented in this manuscript and associated materials does not necessarily reflect the views or policies of NIST or the United States Government. N.G. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences through Award No. KC030105172685. This research benefited from computational resources provided by the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at PNNL. PNNL is operated by Battelle Memorial Institute for the United States Department of Energy under DOE Contract No. DE-AC05- 76RL1830. We thank Professor Brandi Cossairt and Professor Munira Khalil of the University of Washington for useful discussions. We thank Dr. Drew Pomerantz for providing some of the sulfur compounds considered in this paper.