Resonance photoemission forf-electron systems

We develop a theory for resonance photoemission and apply it to Ce compounds and ${\mathrm{UO}}_2$ described in a modified Anderson impurity model. For Ce (${\mathrm{UO}}_2$) 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, we derive general formulas for the photoemission spectrum as a function of photon energy. The 1/$N_f$ expansion is then used to obtain explicit results for the Anderson model. All terms of order (1/$N_f$ ${)}^0$ and some terms of order (1/$N_f$ ${)}^1$ are included. The theory is used to explain the different photon-energy dependence for the two peaks in the Ce 4f valence and the ${\mathrm{UO}}_2$ 4f core spectra. We find that interference between different intermediate configurations plays a crucial role.