Bonding state formed between adsorbed benzene and Cu(111)

Two-photon photoemission spectroscopy of a benzene-adsorbed Cu(111) surface has revealed that adsorption-induced occupied and unoccupied electronic st ates are formed at -0.23 and +1.0 eV with respect to the Fermi level. The s tates are assigned to be due to bonding and antibonding orbitals formed by hybridization of benzene pi-orbital and copper s.p orbitals. The bonding st ate, which is difficult to identify with UPS, is greatly enhanced by resona nce with the image potential state. The photoemission intensity of the bond ing state has been measured asa function of photon energy. The excitation e fficiency curve shows that the resonance enhancement factor is more than 10 0, and the resonance width is less than 0.15 eV. However, bulk states or th e occupied copper surface state showed no resonance with the image state of a benzene-covered surface area. (C) 2000 Elsevier Science B.V. All rights reserved.