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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 e2u level of benzene into b1 and a2 levels for pyridine and into b3u and au levels for pyrazine; the corresponding <em>π</em> resonances are asymmetric due to the vibrational fine structure. At the nitrogen K-edge the transitions into the a2 and au 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 <em>π</em> resonances are considerably broadened at the adsorption edges of atoms which interact strongly with the substrate.
