The authors develop a theory for resonance photoemission and apply it to Ce compounds and UO2 described in a modified Anderson impurity model. For Ce (UO2) the model takes into account decay processes involving two 4f (5f) electrons, one 4f (5f) electron, and a core electron. Starting from the quadratic response formalism, they derive general formulas for the photoemission spectrum as a function of photon energy. The 1/Nf expansion is then used to obtain explicit results for the Anderson model. All terms of order (1/Nf)0 and some terms of order (1/Nf)1 are included. The theory is used to explain the different photon-energy dependence for the two peaks in the Ce 4f valence and the UO2 4f core spectra. It is found that interference between different intermediate configurations plays a crucial role.
 

Physical Review B, 36 9488-99, 1987.