CO adsorption on Pd(111): a high-resolution core level photoemission and electron energy loss spectroscopy study

By combining high-resolution X-ray photoelectron and electron energy loss spectroscopies a comprehensive analysis of the adsorption of CO on Pd(1 1 1) at 300 K has been performed. The characteristic fingerprints for various CO‐ Pd(1 1 1) bonding configurations have been identified from the decomposition analysis of the adsorbate C 1s and the substrate Pd 3d5=2 core-level photoemission spectra obtained after CO adsorption at 120 K. The cO4 2U structure at 0.5 monolayer (ML) and theO2 2U-3CO structure at 0.75 ML formed at low temperature have been used for calibration purposes. The core-level results are consistent with CO adsorbing in a mixture of fcc and hcp threefold hollow sites in the cO4 2U structure and of hollow and on-top sites in theO2 2U structure, as reported in the literature. For CO adsorption at 300 K, a diAerent site occupation is evidenced by the presence of two components in the C 1s and Pd 3d5=2 core-level and C‐O stretching vibration lineshapes. At coverages up to 0.1 ML only fcc threefold hollow sites in a O AAA

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