SO2-INDUCED SURFACE RECONSTRUCTION OF Cu{111} STUDIED BY X-RAY-ABSORPTION FINE-STRUCTURE
M.Polcik, L.Wilde and J.Haase
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin-Dahlem , Germany
Keywords: metal surfaces, molecular adsorption,SO2, surface reconstruction, synchrotron
SO2 exhibits interesting bonding properties in transition metal compexes with a large diversity of binding modes which have been characterised by the metal-S(O) and the intramolecular S-O bond lengths, by the O-S-O bond angle and by vibrational frequencies [1]. Compared to the detailed knowledge of the coordination chemistry, rather little information has been available on the SO2-surface complexes [2].
The adsorption of SO2 on the Cu{111} surface has been studied by means of the surface-extended x-ray-absorption fine structure (SEXAFS) and the near-edge x-ray-absorption fine structure (NEXAFS) above the Oxygen and Sulphur K absorption edges. These techniques reveal aspects of SO2 interaction with metal surfaces. As has been shown earlier [3] SO2 adsorption on Cu{111} at 170K results in an (SO2+O) coadsorption phase with additional negligible amounts of SO and atomic S. The SEXAFS and NEXAFS indicate that on SO2 adsorption the Cu{111} surface undergoes a reconstruction. The data suggest that the S atoms of SO2 are positioned in fourfold hollow sites on a locally {100} reconstructed Cu{111} surface.The molecular plane is oriented nearly perpendicular to the surface. Within this plane the molecule is tilted which is attributed to an O-Cu bonding interaction in addition to bonding to the substrate through the S-atoms.