Multiplet effects in the Ru $L_{2,3}$ x-ray-absorption spectra of Ru(IV) and Ru(V) compounds

We report combined experimental and theoretical investigations of x-ray absorption at the $\mathrm{Ru}{-L}_{2,3}$ and O-K thresholds of the Ru(IV) compounds ${\mathrm{RuO}}_2$ and ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and of the Ru(V) compound ${\mathrm{Sr}}_4{\mathrm{Ru}}_2{\mathrm{O}}_9.$ Significant differences in the intensity distribution of the $t_{2g}$-related and $e_g$-related peaks between the $L_3$ and the $L_2$ edges are found, due to the combined effects of $4d$ spin-orbit coupling and the interelectronic Coulomb interaction described by the Slater integrals. The observed spectral features can be well reproduced by crystal-field-multiplet calculations. With increasing the Ru valence from IV to V, the spectra are shifted by ≅1.5 eV to higher energy at the $\mathrm{Ru}{-L}_{2,3}$ edges and ≅1.0 eV to lower energy at the O-K edge, which is of the same order of magnitude as on going from the divalent to the trivalent late $3d$ transition-metal oxides.