X‐ray photoemission studies of the electronic structure of rare earth metals

X‐ray photoemission (XPS) measurements are reported on evaporated films of the rare earth metals Eu, Gd, and Yb. For comparison additional measurements are reported on Ba. The results provide an unambiguous determination of the 4f energy levels. In Yb the spin–orbit splitting is also clearly resolved. The locations of the 4f levels below the Fermi level are determined to be 2.1 eV for Eu, 7.7 eV for Gd, and 1.4 eV and 2.7 eV for Yb all with an error of ± 0.4 eV.