Extracting Chemistry From Core-Level Spectroscopies: Combining Theory And Experiment

Paul S. Bagus,¹ and Connie J. Nelin,^2
1Department of Chemistry, University of North Texas, Denton, Texas 76203-5017, USA
²Consultant, Austin, Texas 78730, USA

The goal of X-Ray Photoelectron Spectroscopy, XPS, and X-Ray Adsorption Near Edge Spectroscopy, XANES, is to obtain information about the chemical interactions and bonding in the compound studied. With modern computational resources, theorists can obtain XPS and XANES energies and intensities that compare favorably with measured spectra. Experimentalists can obtain XPS and XAS spectra for a variety of samples, sometimes to be compared with theoretical results. However, rather than examine the XPS and XAS of individual systems, another approach involves varying materials and, especially for theorists, varying parameters since this may allow the physical and chemical mechanisms responsible for the observed features to be identified and related to the chemistry of the material. Theorists have a special advantage in that it is straightforward to vary bond distances and electronic states and to vary the level of the theoretical treatment of the wavefunctions. However, it is necessary to use special methods for the analysis of the molecular orbitals and wavefunctions that go beyond the usual Mulliken Population Analysis. There are several critical contributions from experimentalists including identifying suitable systems for joint studies, making suitable measurements, and assessing the reliability of the measurements. The type of information that can be obtained will be discussed for representative systems that have been studied in collaborations between the authors and their experimental colleagues. This will include analysis of XPS BE shifts and the chemical significance of the shifts, the XPS of ionic Ni(II) compounds with different ligands.

PSB acknowledges supported of the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences (CSGB) Division through its Geosciences program at Pacific Northwest National Laboratory (PNNL).