Structure of Cytosine on Cu(110): a Scanned-Energy Mode Photoelectron Diffraction Study

The local adsorption structure formed by the interaction of cytosine with a Cu(110) surface, following adsorption at similar to 300 K and annealing to similar to 420 K, has been investigated by O 1s and N 1s scanned-energy mode photoelectron diffraction (PhD). Initial characterization by soft-X-ray photoelectron spectroscopy and O K-edge near-edge X-ray absorption fine structure (NEXAFS) indicates that chemisorption leads to dehydrogenation of the NH species in the molecular ring and indicates that the molecular plane is perpendicular to the surface and close to the [1 (1) over bar0] azimuth. The PhD results confirm this orientation and show that the molecule bonds to the surface through the deprotonated N atom and the O atom, both of which occupy off-atop sites. The associated Cu-N and Cu-O bondlengths are 1.94(+0.07/-0.03) angstrom and 1.94(+0.06/-0.04) angstrom, respectively. Density functional theory calculations provide further support for this local structure and provide information on the possible role of intermolecular interaction. Possible structural models accounting for previously observed long-range ordered phases with glide symmetry are discussed in the light of these results.