  Valence band electronic structure of mixed uranium oxides (UO2, U4O9, U3O7,
U3O8, UO3) has been studied by the resonant inelastic X-ray scattering (RIXS)
technique at the U M5 edge and by computational methods. We show here that the
RIXS technique and recorded U 5f-O 2p charge transfer excitations can be used
to proof the validity of theoretical approximations
