Photoemission from atomic and molecular adsorbates on Rh(100)

Using synchrotron radiation as the excitation source, we have measured photoemission spectra of the valence and core levels of clean and adsorbate-covered Rh(100). The surface core level shift (SCLS) of clean Rh and the adsorbate-induced SCLSs due to oxygen, hydrogen, NO and CO are discussed in the light of recent calculations. The shift due to CO is anomalous and less than that predicted from thermodynamic data and a Born-Haber cycle. In addition, angle-resolved photoemission spectra from the oxygen-induced (2 x 2)p4g structure have been measured at the Cooper minimum of the Rh 4d band. The results have been analyzed to yield the surface band structure of oxygen-induced states, without interference from Rh substrate peaks. A strong photoemission feature tentatively assigned to O p(z) derived states is found to disperse over a range of 1.4 eV.