LEED intensity analysis of the structures of clean Pt(111) and of CO adsorbed on Pt(111) in the c(4 × 2) arrangement

Abstract

The surface structures of clean Pt(111) and CO adsorbed on Pt(111) with c(4 × 2) periodicity at one-half monolayer coverage were investigated by a dynamical LEED intensity analysis of measured I-V curves. The clean Pt(111) structure is confirmed to be nearly indistinguishable from the truncated bulk structure (within ≈ 0.025 Å). The c(4 × 2) unit cell contains one CO molecule adsorbed on a top site and one CO molecule adsorbed on a bridge site, both molecules being perpendicular to the surface. This is only the second LEED structure determination of multi-site molecular adsorption. The CO molecules have metal-carbon bond lengths of 1.85 ± 0.1 and 2.08 ± 0.07 Å for the top and bridge sites, respectively, and the same carbon-oxygen bond length of 1.15 ± 0.05 Å. Trends relating bond lengths and vibration frequencies for CO adsorption on various metal surfaces are presented. In particular, the CO stretch frequency decreases as the metal-carbon bond length increases, which in turn increases as the carbon-metal coordination number increases.