Zhejiang Univ, Dept Phys, Hangzhou 310027, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Lab Synchrotron Radiat, Beijing 100039, Peoples R China
The molecular orbits of CO are rearranged under the strong influence of coadsorbed Cs atoms. The peak for CO on clean Ru(10 (1) over bar 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. The former peak shows an antisymmetry character about the plane parallel to the  crystallographic direction in the surface.