High resolution NEXAFS studies of aromatic molecules adsorbed and condensed on Ni(111)

Abstract High resolution near-edge X-ray absorption fine structure measurements have been performed on benzene, pyridine and pyrazine adsorbed and condensed on Ni(111). The carbon K-edge multilayer data show the splitting of the e 2u level of benzene into b 1 and a 2 levels for pyridine and into b 3u and a u levels for pyrazine; the corresponding π resonances are asymmetric due to the vibrational fine structure. At the nitrogen K-edge the transitions into the a 2 and a u levels are not observed. The benzene data suggest that the Rydberg orbitals are quenched in the condensed phase and that the broad structure above a photon energy of ∼300 eV is made up of (at least) two σ resonances. On adsorption the π resonances are considerably broadened at the adsorption edges of atoms which interact strongly with the substrate.