HREEIS Stodies of Oxygen Adsorption on the Cs and CO Coadsorbate Precovered Ru(0001) Surfact

Oxygen adsorption on the Cs and CO coadsorbate precovered Ru(0001) surface was studied by means of high-resolution electron-energy-loss spectroscopy（HREELS）. At zero Cs coverage, i.e., in the case of O+CO coadsorption, oxygen adsomtion leads to weaking of surface bond of CO resulting from the repulsive interaction betwee CO molecules and O adatoms, and CO molecules and O adatoms form a mixture phase. For the submonolayer Cs coverage, an appropriate amount of CO adsorption leads to formtion of （2 × 2）-Cs+2CO islands. Subsequent oxygen adsorption on this Cs+CO coadsorbate precovered surface results dramatic change in HREEL spectra. The loss peak of C-O stretch mode for （2 ×2）-Cs + 2CO island species decreases in intensity,which was accompanied by appearance of new bands at about 87 and 240meV （bare stirface CO）. The results show that Cs adatoms and CO molecules are rearranged upon oxygen adsorption, and are correlated with coexistence of bare surface CO and mixed Cs +CO+O phase. CO saturation on the Cs precovered surface at any Cs coverage makes the surface inactive for dissociative adsorption of O₂.