Valence-band photoemission inUO2(111) near the5dresonant photon energy

Pronounced Fano-like resonant effects are observed in the photoemission spectra of the localized U 5f and O?p ndash—U?f,6d— bonding bands of ${\mathrm{UO}}_2$ when photon energies near the U 5$d_{3/2}$,5/2 thresholds (105 and 97.1 eV, respectively) are employed. The constant-final-state spectra are well described by calculated transition energies and oscillator strengths for the 5$d^{10}$5$f^2$ ${\to }^{h\nu }$5$d^9$5$f^3$ process; also, the decay rates of the intermediate-state multiplets are in qualitative agreement with the observed width of the spectral features. Distinctly different constant-initial-state (CIS) spectra are obtained at the intensity maximum of the U 5f photopeak and at the minimum between the 5f peak and the O 2p bonding band. Calculated decay rates indicate that this results from variations in the branching ratio for decay of intense intermediate-state multiplets into ${}_{}{}^2{}_{}{}^{}\mathrm{F}_{5/2}^{}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{F}_{7/2}^{}{}_{}{}^{}$ final states. Resonant effects in the O?p ndash—U?f,6d— bonding band show the bonding participation of U orbitals; moreover, the higher intensity of the CIS spectrum obtained near the top of the bonding band agrees with band-structure calculations showing most of the U 5f character in this region.