The interaction of SO2 with Cu(111) was studied by X-ray-absorption fine-structure measurements above both the oxygen and sulfur K edge. The combined analysis of the data for the (SO2+O) phase formed on adsorption of SO2 at 170K showed that the S atoms were located in hollow sites on a locally (100) reconstructed surface with a S-Cu bond length of 2.32Å. The SO2 molecular plane was oriented perpendicular to the surface. Within the plane the C2 axis was tilted with respect to the surface normal resulting in additional bonding to the substrate through one of the oxygen atoms. The corresponding O-Cu bond length measures 2.14Å. Due to bonding through only one of the oxygen atoms two different intramolecular bond lengths, 1.43 and 1.48Å, within the same molecule were observed. The co-adsorbed atomic oxygen was located in bridge sites with a O-Cu bond length of 2.02Å. These results were consistent with a structural model where (100) units formed a so-called clock reconstruction.

SO2-Induced Surface Reconstruction of Cu(111) - an X-Ray Absorption Fine-Structure Study. M.Polčik, L.Wilde, J.Haase: Physical Review B, 1998, 57, 1868-74