It is also possible to record the emitted characteristic fluorescence as a function of the excitation energy, resulting in a spectrum that is similar to XANES. The main difference is there being a two-step process involving excitation of an electron (3d→5f/7p) and subsequent emission of a photon (4f→3d). Consequently, there are two core-holes involved in the excitation process, namely 3d (intermediate state) and 4f (final state) (cf. Figure ). The recorded fluorescence intensity, plotted against the excitation energy, constitutes a core-to-core RIXS (CC-RIXS) map. The Pu M 5 -edge HR-XANES spectra (equivalent to HERFD-XANES spectra) are a cross section of this RIXS map at fixed emission energy as previously described for PuO 2 . The Pu M 5 -edge HR-XANES probes the unoccupied Pu 5f and 7p density of states in a presence of the 4f core-hole in the final state. The Pu M 5 -edge VB-RIXS describes electronic excitations from the 3d shell to the 5f/7p unoccupied states (3d→5f/7p) followed by transitions of 5f electrons from the occupied valence band filling the created 3d core-hole (5f part of valence band→3d) (cf. Figure ). Thus the VB-RIXS process follows also a two-step process involving core 3d exciton (intermediate state, IS) and valence exciton (valence-band final-state, VB-FS).