High-energy spectroscopy of fn+1 and fn−1 states in rare earth metals

Two different spectroscopies have been used to study the 4f shell in rare earth metals. The spectra obtained by X-Ray Photoemission Spectroscopy (XPS) reflect the final states resulting from the transitions fn→fn−1; in Bremsstrahlung Isochromat Spectroscopy (BIS) the recorded intensity of x-rays accounts for the transitions fn→fn+1. The analysis of the two types of spectra of one element with initial configuration 4fn yields an exact determination of the excitation energies Δ− and Δ+ to the ground states of fn−1 and fn+1. The experimental energies are related to EF and correspond to completely screened final states of the metals. (Δ+−Δ−) can be interpreted as the screened Coulomb correlation energies U which is very large in these metals (5–12 eV) and prevents the formation of a band.