| Abstract
| - We have studied enantiospecific differences in the adsorption of (S)- and (R)-alanine on Cu{531}R usinglow-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, and near edge X-ray absorptionfine structure (NEXAFS) spectroscopy. At saturation coverage, alanine adsorbs as alaninate forming ap(1 × 4) superstructure. LEED shows a significantly higher degree of long-range order for the S than for theR enantiomer. Also carbon K-edge NEXAFS spectra show differences between (S)- and (R)-alanine in thevariations of the π resonance when the linear polarization vector is rotated within the surface plane. Thisindicates differences in the local adsorption geometries of the molecules, most likely caused by the interactionbetween the methyl group and the metal surface and/or intermolecular hydrogen bonds. Comparison withmodel calculations and additional information from LEED and photoelectron spectroscopy suggest that bothenantiomers of alaninate adsorb in two different orientations associated with triangular adsorption sites on{110} and {311} microfacets of the Cu{531} surface. The experimental data are ambiguous as to the exactdifference between the local geometries of the two enantiomers. In one of two models that fit the data equallywell, significantly more (R)-alaninate molecules are adsorbed on {110} sites than on {311} sites whereas for(S)-alaninate the numbers are equal. The enantiospecific differences found in these experiments are muchmore pronounced than those reported from other ultrahigh vacuum techniques applied to similar systems.
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