Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 88: Metal substrates: Adsorption of organic / bio molecules IX
O 88.7: Vortrag
Donnerstag, 17. März 2011, 18:45–19:00, PHY C213
Face-dependent chemisorption bondlengths for the formate species on copper. — •Dagmar Kreikemeyer-Lorenzo1, Matt Bradley2, Werner Unterberger1, David Duncan2, Tsenolo Lerotholi2, Jim Robinson2, and Phil Woodruff2 — 1Fritz-Haber-Institut der MPG, Berlin — 2University of Warwick, England
Chemisorption bondlengths of molecules at metal surfaces have been shown in the past to be dependent on the bond order or coordination number according to a Pauling-like relationship, independent of the crystal face. However, we report here the results of measurements that show a rather strong face-dependence. Specifically, we have investigated the adsorption of the formate species (HCOO), a surface intermediate of the catalytic decomposition of formic acid (HCOOH) on Cu (110) and Cu (111) using the well-established technique of scanned-energy mode photoelectron diffraction (PhD). By using the same technique to study the same adsorbate on the two different faces, we eliminate possible sources of systematic error. Formate is found to adopt the same local bridging geometry (with the O atoms in off-atom sites) on both surfaces, but the associated Cu-O bondlengths are found to be 1.99 Å on Cu(111) and 1.90 Å on Cu (110). The difference must be attributed to more open structure of the Cu(110) surface, on which the surface Cu atoms have lower coordination to the underlying bulk and are surrounded by a lower valence charge density due to Smoluchowski smoothing. Preliminary DFT calculations reproduce the effect qualitatively, but predict a significantly smaller bondlength difference.