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Abstract

The structure of the Pd(1 1 0)(2 x 1)-CO ordered adsorption phase has been determined by scanned-energy mode photoelectron diffraction. The CO molecules are adsorbed close to short-bridge sites with alternating tilts along the close-packed <110> surface rows. This local geometry is consistent with that found in previous theoretical total energy calculations and an earlier X-ray photoelectron diffraction study, but is in direct contradiction to the results of an earlier quantitative low energy electron diffraction investigation. While the best-fit model structure involves some twist of the CO molecules out of the <1 0 0> mirror planes of the surface creating a surface phase of p1g1 symmetry, the more symmetric p2mg falls within the estimated limits of precision of the analysis.