Coverage-dependent molecular tilt of carbon monoxide chemisorbed on Pt{110}: A combined LEED and DFT structural analysis

摘要

The adsorption of carbon monoxide on the Pt{110} surface at coverages of 0.5 ML and 1.0 ML was investigatedudusing quantitative low-energy electron diffraction (LEED IV) and density-functional theory (DFT). At 0.5udML CO lifts the reconstruction of the clean surface but does not form an ordered overlayer. At the saturationudcoverage, 1.0 ML, a well-ordered p(2×1) superstructure with glide line symmetry is formed. It was confirmedudthat the CO molecules adsorb on top of the Pt atoms in the top-most substrate layer with the molecularudaxes tilted by ±22° with respect to the surface normal in alternating directions away from the closeudpacked rows of Pt atoms. This is accompanied by significant lateral shifts of 0.55 Å away from the atopudsites in the same direction as the tilt. The top-most substrate layer relaxes inwards by −4% with respect toudthe bulk-terminated atom positions, while the consecutive layers only show minor relaxations. Despite theudlack of long-range order in the 0.5 ML CO layer it was possible to determine key structural parameters byudLEED IV using only the intensities of the integer-order spots. At this coverage CO also adsorbs on atop sitesudwith the molecular axis closer to the surface normal (b10°). The average substrate relaxations in eachudlayer are similar for both coverages and consistent with DFT calculations performed for a variety of orderedudstructures with coverages of 1.0 ML and 0.5 ML.