Electronic structures in the valence region of chemisorbed and physisorbed species on Pd(110)

Electronic structures of CO, CH4 and Xe on Pd(110) were studied by means of photoelectron spectroscopy (PES) using synchrotron radiation. In order to enhance the sensitivity for the adsorbate derived states in valence PE spectra, photon energy at the Cooper minimum (h nu = 120-130 eV) was utilized, In the case of the CO saturated Pd(110) surface at 90 K, peaks are observed at similar to 3.4 eV, 8.0 eV (with a shoulder at similar to 7.2 eV), 11.0 eV and 14.4 eV below the Fermi level (E-F) In addition to the previously reported peaks (1 pi and 5 sigma at similar to 8 eV and 4 sigma at similar to 11 eV), two peaks were newly observed. The 3.4 eV peak could be assigned to the bonding state hybridized between CO 2 pi and Pd 4d orbitals. The 14.4 eV peak is tentatively assigned to the CO 4 sigma shake-up satellite, In the 'physisorption' systems, i.e. CH4 and Xe on Pd(110), only the smooth attenuation of photoemission from the Pd Ad-band was observed in the PE spectra. (C) 1998 Elsevier Science B.V.