Experimental Atom-To-SolidL-Level Shifts for Ce, Sm, Gd, and Er

The x-ray $L$ absorption spectra were measured for the atomic rare-earth elements Ce, Sm, Gd, and Er. From the energy positions of well resolved absorption lines at threshold in comparison to the corresponding solid-state spectra the atom-to-metal shifts of the core-level binding energies have been determined. For Sm and Er which undergo a valence change on formation of the solid the shifts differ by more than 6 eV from those of Ce and Gd which have the same configuration in the atom and the solid.