KβMainline X-ray Emission Spectroscopyas an Experimental Probe of Metal–Ligand Covalency

摘要

The mainline feature in metal Kβ X-ray emission spectroscopy (XES) has long been recognized as an experimental marker for the spin state of the metal center. However, even within a series of metal compounds with the same nominal oxidation and spin state, significant changes are observed that cannot be explained on the basis of overall spin. In this work, the origin of these effects is explored, both experimentally and theoretically, in order to develop the chemical information content of Kβ mainline XES. Ligand field expressions are derived that describe the behavior of Kβ mainlines for first row transition metals with any dⁿ count, allowing for a detailed analysis of the factors governing mainline shape. Further, due to limitations associated with existing computational approaches, we have developed a new methodology for calculating Kβ mainlines using restricted active space configuration interaction (RAS–CI) calculations. This approach eliminates the need for empirical parameters and provides a powerful tool for investigatingthe effects that chemical environment exerts on the mainline spectra.On the basis of a detailed analysis of the intermediate and finalstates involved in these transitions, we confirm the known sensitivityof Kβ mainlines to metal spin state via the 3p–3d exchangecoupling. Further, a quantitative relationship between the splittingof the Kβ mainline features and the metal–ligand covalencyis established. Thus, this study furthers the quantitative electronicstructural information that can be extracted from Kβ mainlinespectroscopy.