Energy shifts of K x-ray lines for different chemical compounds of Ru, Pr, and Yb

The energy shifts of Kα₂, Kα₁, Kβ₃, Kβ₁, and Kβ₂ x rays were measured for the following Ru, Pr, and Yb compounds: Ru, Ru(CO₂)Cl₂, RuO₂, [Ru(NH₃)₄OHCl]Cl · 2H₂O, and RuF₃; Pr, PrC₂, Pr₂O₃, PrFeO₃, Pr₆O₁₁, PrO₂, CsPrF₅, and Cs₂PrF₆, Yb, YbF₃, and Yb₂O₃. The results are compared with free-ion relativistic self-consistent-field calculations. The measurements bear out the dominant role of the $4f$ electrons in energy shifts between the trivalent and tetravalent Pr and the divalent and trivalent Yb. In Yb the full free-ion value is observed, while in Pr the free-ion value appears to be attenuated by a factor of 0.4, presumably owing to covalency. In all cases the relation of the x-ray energy shift to the M\"ossbauer isomer shift is discussed.