The structure of Pt(111)+c(4×2)-2CO has been refined using the powerful capabilities of automated tensor LEED, in particular to determine hitherto-unexplored adsorbate-induced relaxations in the substrate. The refinement considerably improves the fit to experiment obtained in a previous structural analysis performed with low-energy electron diffraction (LEED). This study confirms that CO occupies both top and bridge sites. It finds a buckling of the outermost Pt layer, such that the Pt atoms bonded to CO molecules are raised out of the surface by 0.06±0.04 Å relative to the Pt atoms which do not bond to CO. The raised atoms have a spacing of 2.28±0.04 Å to the next Pt layer, expanded from the bulk spacing of 2.2655 Å, while the depressed Pt atoms have a reduced spacing of 2.22±0.04 Å to the next Pt layer. The second Pt layer itself shows minor buckling of 0.03±0.04 Å. No lateral relaxations in the substrate are detected within 0.1 Å. The CO molecules are perpendicular to the surface, with bond lengths of 1.12±0.04 Å and 1.19±0.04 Å in top and bridge sites, respectively. The C–Pd spacings, measured between bonding atoms, are 1.92±0.04 Å and 1.40±0.04 Å in top and bridge sites, respectively.
