X-ray photoelectron spectra for single-crystal Ti2O3: Experiment and theory

We have measured high-resolution core-level and valence-band x-ray photoemission spectra for single-crystal Ti2O3 cleaved anoxically. The Ti(III) spectra for this lattice are considerably more complex than those measured for Ti(IV)-based oxides due to the presence of a single unpaired electron in the conduction band. This open-shell electron configuration leads to ligand-field split and frequently unresolved multiplets. The Ti 2p and 3p spectra have been calculated using relativistic Dirac-Hartree-Fock (DHF) theory with the sudden approximation for the intensities. Agreement between theory and experiment is excellent for the 3p spectrum, and very good for the 2p spectrum, the primary deficiency being a pair of features not captured by theory for the latter. The spectral line shapes are driven by final-state effects associated with angular momentum coupling of the unpaired valence electron with the core hole, one-and two-electron ligand-to-metal charge-transfer (shake) processes accompanying core photoionization, and core-hole screening by conduction-band electrons. The first two of these are accurately predicted by DHF theory with a small embedded cluster containing a single Ti cation and six oxygen ligands. The third effect is not predicted using this cluster in which screening of the core hole from electrons associated with more distant atoms is not possible.