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 investigating
the effects that chemical environment exerts on the mainline spectra.
On the basis of a detailed analysis of the intermediate and final
states involved in these transitions, we confirm the known sensitivity
of Kβ mainlines to metal spin state via the 3p–3d exchange
coupling. Further, a quantitative relationship between the splitting
of the Kβ mainline features and the metal–ligand covalency
is established. Thus, this study furthers the quantitative electronic
structural information that can be extracted from Kβ mainline
spectroscopy.