Extreme Ultraviolet Photoemission of CeB6 and PrB6

Photoelectron spectra of CeB 6 and PrB 6 have been measured over the excitation-energy range from 30 to 140 eV. From the locations of the peaks which grow resonantly upon excitation in the giant absorption bands above the 4 d thresholds of rare earths, the binding energies of 4 f electrons in resonance are found to be 2.5 eV in CeB 6 and 4.7 eV in PrB 6 . The shapes of energy distribution curves observed by excitation below resonance agree with the reported energy distribution curve of LaB 6 and with the density-of-states curve calculated on LaB 6 by the Xα-APW method. A sharp peak is resolved at the Fermi edge of CeB 6 . Its origin is discussed in relation to valence fluctuation.