Study of the4fLevels in Rare-Earth Metals by High-Energy Spectroscopies

The density of the $4f$ states in all metallic rare earths has been studied with bremsstrahlung isochromat spectroscopy (BIS) and x-ray photoemission spectroscopy (XPS). The final-state multiplet structures of the $4f^{14-n}$ and $4f^n$ configurations observed by BIS and XPS, respectively, are closely related. The elements showing interconfiguration fluctuations are found to have one $4f$ level in the immediate vicinity of the Fermi level. Correlation energies are extracted directly from the spectra and compared with recent theoretical calculations.