Multiplet effects in the RuL2,3x-ray-absorption spectra of Ru(IV) and Ru(V) compounds

We report combined experimental and theoretical investigations of x-ray absorption at the $\mathrm{Ru}{\ensuremath{-}L}_{2,3}$ 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 \ensuremath{\cong}1.5 eV to higher energy at the $\mathrm{Ru}{\ensuremath{-}L}_{2,3}$ edges and \ensuremath{\cong}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.