We consider two different resonant X-ray emission spectra for Ce compounds: Ce 3d to 2p X-ray emission (denoted by 3d-RXES) and valence to 2p X-ray emission (v-RXES), both of which follow the Ce 2p to 5d resonant excitation. We propose that the comparison of the 3d- and v-RXES spectra is a new powerful method of directly detecting the core-hole effect in the final state of Ce L 3 X-ray absorption spectra (XAS). We applied this method to recent experimental RXES spectra for CeO 2 and CeFe 2, and showed unambiguously that the core-hole effect should be essential in the XAS of both materials. This result is confirmed by theoretical calculations, which reproduce well the experimental RXES and XAS spectra. We conclude that the ground state of CeO 2 is in the mixed state of 4f0 and [Formula: see text] configurations, where [Formula: see text] is a ligand hole, instead of a pure 4f0 configuration which was proposed recently by first-principles energy band calculations. Also, we conclude that the double peaks observed in L 3 XAS of CeFe 2 are caused by the 4f0 and 4f1 configurations, which are mixed in the ground state but separated in energy by the large core-hole potential in the final state of XAS.
Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene