Probing Valence Orbital Composition with Iron Kβ X-ray Emission Spectroscopy

A systematic study of 12 ferric and ferrous Kβ X-ray emission spectra (XES) is presented. The factors contributing to the Kβ main line and the valence to core region of the spectra are experimentally assessed and quantitatively evaluated. While the Kβ main line spectra are dominated by spin state contributions, the valence to core region is shown to have greater sensitivity to changes in the chemical environment. A density functional theory (DFT) based approach is used to calculate the experimental valence spectra and to evaluate the contributions to experimental intensities and energies. The spectra are found to be dominated by iron np to 1s electric dipole allowed transitions, with pronounced sensitivity to spin state, ligand identity, ligand ionization state, hybridization state, and metal−ligand bond lengths. These findings serve as an important calibration for future applications to iron active sites in biological and chemical catalysis. Potential applications to Compound II heme derivatives are highlighted.