Different bonding configurations of the aromatic anhydride NDCA on Ni(111) and O/Ni(111): A photoemission and TDS study

The adsorption of the planar aromatic molecule NDCA (naphthalene-3,4-dicarboxylic anhydride) on clean and oxygen-precovered Ni(111) has been studied by thermal desorption spectroscopy (TDS) and by X-ray and UV photoelectron spectroscopy. For both substrates all spectroscopic data allow a clear distinction between multi-, bi-, and monolayer. In the monolayer regime we found in each case two different adsorption states which differ in bonding strength, orientation, and desorption behaviour and are strongly temperature dependent. On the O-precovered substrate both TDS and photoelectron spectra exhibit remarkable changes in comparison with the spectra of NDCA on the clean surface, indicating a strongly modified coupling, induced by the interaction between the anhydride group and the O-p(2 x 2) coadsorbate. Further insight into the electronic structure of NDCA and the adsorbate-substrate interaction is provided by the comparison of UP spectra and semiempirical calculations.