Pressure-induced changes in $L_{\mathrm{III}}$ x-ray-absorption near-edge structure of Ce${\mathrm{O}}_2$ and Ce${\mathrm{F}}_4$: Relevance to $4f$-electronic structure

X-ray-absorption near-edge structure (XANES) studies were performed at the $L_{\mathrm{III}}$ thresholds of Ce${\mathrm{O}}_2$ and Ce${\mathrm{F}}_4$ as a function of external pressure up to ≅267 kbar at room temperature. In both cases, the ${4f}^0$-related higher-energy component of the essentially double-peaked XANES structure decreases in relative intensity with pressure, opposite to what is generally observed for metallic mixed-valent Ce compounds. This supports the proposed peak assignment on the basis of core-hole induced many-body effects due to $4f$-ligand covalency compatible with traditional tetravalency of these compounds.