SO₂-induced surface reconstruction of Cu(111): An x-ray-absorption fine-structure study

The interaction of SO2 with Cu(111) has been 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 170 K shows that the S atoms are located in hollow sites on a locally (100) reconstructed surface with a S-Cu bond length of 2.32±0.05Å. The SO2 molecular plane is oriented perpendicular to the surface. Within the plane the C2 axis is 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 2.14±0.05Å. Due to bonding through only one of the oxygen atoms two different intramolecular bond lengths, 1.43±0.03 and 1.48±0.03Å, within the same molecule are observed. The coadsorbed atomic oxygen is located in bridge sites with a O-Cu bond length of 2.02±0.05Å. These results are consistent with a structural model where (100) units form “clock” reconstruction