Hydrogen-induced change in the4flocalization inCeRu2studied with x-ray photoemission spectroscopy

Our x-ray photoemission spectroscopy study of ${\mathrm{CeRu}}_2$ ${\mathrm{H}}_{\mathrm{\approxeq }4}$ shows the disappearance of a Ce 3d satellite peak which is generally at- tributed to an $f^0$ final state and a reduction of the $f^2$-final-state-related intensity. An interpretation in terms of an Anderson model leads to an increase in the f count $n_f$ from ≊0.8 to nearly unity and to a change in the 4f–conduction-band hybridization energy Δ from 120 meV to 60±20 meV. The observed binding-energy shifts of 0.7 eV (Ce 3d, 5p) and 0.4 eV (Ru 3d) are partly due to the lattice expansion as the 4f bonding contribution disappears. The valence-band spectrum shows weak hydrogen-induced emission at 5–8 eV. The observation of peaks at ≊1 eV and ≊2.6 eV in ${\mathrm{CeRu}}_2$ and ${\mathrm{CeRu}}_2$ ${\mathrm{H}}_{\mathrm{\approxeq }4}$, respectively, fits well into the $f^1$-$f^0$ screening scheme.