Width of the $d$-Level Final-State Structure Observed in the Photoemission Spectra of ${\mathrm{Fe}}_x\mathrm{O}$

X-ray photoemission (XPS) measurements of wustite, ${\mathrm{Fe}}_x\mathrm{O}$ ($x=0.90-0.95\mathrm{}$), show that the Fe ($3d$) valence-band final states spread ∼10 eV below $E_{\mathrm{F}}$. This is much broader than previous claims based on the analysis of lower-energy (5-90 eV) photoemission spectra. Crystal-field-theory results, based on ab initio calculations, are consistent with the broader spectrum. Configuration interaction is found to have important consequences for the position and intensity of the XPS peaks.