Extreme Ultraviolet Absorption Spectra of Barium and Rare Earth Metals

Optical absorption spectra of Ba and rare earth metals have been measured over the photon energy range from 10 to 40 eV. The spectra for Ba do not show Fermi edge singularity as observed in Cs metal. It is found that the energy broadening of the 5 p absorption threshold depends systematically on the atomic number and particularly on the number of 4 f electrons. It is suggested that the potential of the photo-produced 5 p hole induces the virtual localization of 5 d electrons and this enhances the interaction between 5 d and 4 f electrons appreciably.