  X-ray absorption and resonant X-ray emission measurements at the O 1s edge of
the uranium oxides UO2, U3O8 and UO3 are presented. The spectral shapes of the
O K{\alpha} X-ray emission spectra of UO3 exhibit significant excitation energy
dependence, from an asymmetric to a symmetric form, which differs from those of
UO2 and U3O8. This energy dependence is attributed to a significant difference
in the oxygen-uranium hybridization between two different sites in the crystal
structure of UO3. The spectral shapes of UO2 and U3O8 are also found to be
different but without significant energy dependence. The experimental spectra
of the valence and conduction bands of the uranium oxides are compared to the
results of electronic structure calculations available in the literature.
