The surface-extended X-ray absorption fine structure (SEXAFS) spectrum of an electrochemically deposited adlayer of copper on a gold(lll) electrode immersed in solution and under potential control was obtained by employing fluorescence detection and grazing incidence geometry. The X-rays were polarized parallel to the plane of the gold surface. Two peaks were observed in the radial distribution function, indicating two different near neighbors for copper. The near neighbors were determined to be gold at 2.58 ± 0.03 Á and copper at 2.92 ± 0.03 A. The copper-copper distance is identical with the gold-gold lattice spacing, showing that at full coverage the copper adlayer forms a 1X1 commensurate layer on the gold(lll) substrate. The intensity of the gold-copper scattering relative to the copper-copper scattering suggests the copper atoms sit in 3-fold hollow sites.

was taken at the same time. The OWG electrode had sheet resistance of ca. 500 fi/cm1 2 and donor density of ca. 102O/cm3 ([SbCl3] in the spray solution = 2.5 wt %); the optical path length was 1 cm.

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K (on the NMR time scale of a few milliseconds) whereas the multicarbonyls are motionally averaged. The absolute population of each type of adsorbed CO is directly obtained from the integrated intensity. The morphology of the metal particles can be inferred from the CO site distributions, the overall CO-to-metal ratio, and the local density of CO. The particles on a Rh/silica sample prepared by incipient wetness have a local coverage of 0.75, consistent with the saturation coverage measured on Rh[l 11], and are either small spherical (or cuboctahedral) clusters of diameter 15 A, rafts approximately 1.5 layers thick, or a combination.Three catalysts prepared by amine exchange had CO-to-metal ratios greater than 0.75, but the T2's indicate CO-CO densities comparable to the less-dispersed catalyst. We hypothesize that these particles are smaller (5-8 A) and resemble metal carbonyl clusters or small rafts with multiple absorption at the edge metal atoms.This study demonstrates the potential of 13C NMR spectroscopy to characterize a catalytic surface by quantitative analysis of the site distribution of probe molecules. Moreover, the quantitative analysis is not compromised by changes in absorption cross sections (e.g., with electron or vibrational spectroscopies), which may vary nonlinearly with coverage, site, and surface properties.

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