Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R China
; Acad Sinica, Inst High Energy Phys, Lab Synchrotron Radiat, Beijing 100039, Peoples R China
The molecular orbitals of CO are rearranged under the strong influence of coadsorbed Cs atoms. The peak for CO on the clean Ru(10(1)over-bar-0) surface, at 7.5 eV BE attributed to the 5 sigma and Ix orbits, is split into two peaks; one is at 6.3 eV BE and the other 7.8 eV BE. The peak at 6.3 eV BE shows an anti-symmetry character about the plane parallel to the  crystallographic direction in the surface.