Energy dependence of 4fand 5dcross sections for rare-earth metals

We present results on the transition probabilities in isochromat inverse photoemission (hν=10–25 eV) from La, Eu, and Lu together with selected photoemission results (10.8–40.8 eV). While the contribution of the empty 4f states to the inverse photoemission spectra is extremely small in Eu, it is sizeable in La even at the lowest investigated energies. In inverse photoemission the energy dependence of the intensity ratio ${\mathit{I}}_{\left(4\mathrm{}\mathit{f}\right)}$/${\mathit{I}}_{\left(5\mathrm{}\mathit{d}\right)}$ and the trend of the 5d intensity with respect to a Pt reference are presented and a resonant enhancement of the 5d empty-states signal associated with the 5p threshold is observed. The energy dependence is discussed in connection with the available results on occupied and empty electron states obtained by means of different spectroscopies.