Characterization of CO Binding Sites on Rh(111) and Rh(331) Surfaces by XPS and LEED (Low Energy Electron Diffraction): Comparison to EELS (Electron Energy Loss Spectroscopy) Results

摘要

Changes in the nature of the binding site of chemisorbed carbon monoxide on the Rhodium(111) and Rhodium(331) single crystal surfaces during absorption and desorption have been monitored by X-ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED). Two bonding states of molecular carbon monoxide have been identified from the O 1s photoemmission line. These states are assigned as atop and bridge-bonded species and are observed to be coverage and temperature dependent. On both surfaces atop sites are populated first and at higher CO coverages bridge sites are filled. On Rh(111) the bridge sites are filled at a carbon monoxide coverage of theta co approx. 0.50 and their presence is correlated with a change in the LEED pattern. The presence of the step atoms on the Rh(331) surface markedly influenced the sequential filling of binding sites in comparison to that observed on the Rh(111) surface. A comparison of our data to previous Electron Energy Loss Spectroscopy (EELS) work on Rh(111) is in remarkable quantitative agreement with EELS peak heights.