Width of the d-level final-state structure observed in the photoemission spectra of FexO

X-ray photoemission (XPS) measurements of wustite, FexO (x=0.90-0.95), show that the Fe (3d) valence-band final states spread ∼10 eV below EF. 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. © 1977 The American Physical Society.