Studies on Adsorption System of Carbon Monoxide on Cs/\mathrmRu(10 \overline1 0) Surface by Using Synchrotron Radiation

The molecular orbits of CO are rearranged under the strong influence of coadsorbed Cs atoms. HREELS study shown that there are two molecular adsorption states of CO on a Cs pre-covered \mathrmRu(10 \overline1 0) surface. One with high \mathrmC-\mathrmO stretch frequency similar to that on clean \mathrmRu(10 \overline10) surface, the other with low \mathrmC-\mathrmO stretch frequency due to the strong short-range interaction between the CO molecule and the Cs atom. ARUPS experiment results shown the peak for CO on clean \operatornameRu(10 \overline1 0) surface, at 7.5 eV BE attributed to the 5 \sigma and 1 \pi orbits, is split into two peaks with one at 6.3 eV BE and the other at 7.8 eV BE . Two concrete models has been proposed to describe the short-range alkali metal- CO interaction, the \mathrmsp^2 rehybridization model and the direct interaction model. The experiment results confirm that the \mathrmsp^2 rehybridization model must be reasonable. According this model, the \mathrmMe-\mathrmCO bond rehybridizes to \mathrmsp^2 forming new \sigma and \pi bonds ( \mathrma_1, \mathrm~b_1, \mathrm~b_2 orbits in the \mathrmC_2 v point group) According The p -polarized ARUPS results, the peak at 6.3 eV BE, comes from one of a \pi type 1 \mathrm~b_2 orbits, shows an anti-symmetry character about the plane parallel to the <0001> crystallographic direction in the surface. Another \pi type orbit 1 \mathrm~b_1 is still at 7.8 eV BE overlapping with 5 \mathrma_1 orbit.