INTERACTIONS OF NO IN DIFFERENT BINDING STATES WITH COADSORBED CO ON RU(001)

Five different adsorbed states of NO on Ru(001) at 120 K were discrimi nated by HREELS in the range of 680-1820 cm(-1). The two losses at 680 and 1130 cm(-1) are attributed to unusually low-frequency nu(N-O) mod es of molecular states of adsorbed NO: (i) with the N-O bond parallel to the surface and (ii) in upright position bound via the O atom to th e surface, respectively. CO post-adsorption induces a complete convers ion of both states to the threefold coordinated v(0)-NO, already at 12 0 K. The other three NO states appearing at higher coverages respond t o the influence of coadsorbed CO by transformations of one into anothe r and correlate with changes of the ordered structures on the surface. The most stable NO state regarding the CO coadsorption is the threefo ld v(1)-NO. Adsorption of NO on a perfect (root 3 X root 3)R30 degrees layer on Ru(001) leads to a new (2 X 2) symmetry of the coadsorbate l ayer.