Giant Resonance Enhancement of the4f,5p, and5sStates in the Photoemission Spectra of Rare-Earth Compounds

We have measured photoemission from the valence band and outer core levels of rare-earth (Ce, Gd, La) pentaphosphates. Varying the photon energy through the region of the giant resonance of the $4d$ cross section ($h\nu =100-200\mathrm{}$ eV), we find a dramatic enhancement of the rare-earth-derived states ($4f, 5p, 5s$) in the energy distribution curves. This enhancement is explained as due to a strong interaction of the $4d^{9}4f^{n+1\mathrm{}}$ configuration with such other configurations as, e.g., $4d^{10}4f^{n-1\mathrm{}}\epsilon l$ (autoionization).