Coadsorption of nitric oxide and benzene on Ru(001)

The coadsorbate system NO + benzene has been studied on Ru(001) at various relative coverage ratios using HREELS, ΔΦ, TPD and LEED. A strong mutual influence of the two molecules is found as indicated by appreciable shifts of the vibrational frequencies. Benzene retains C_6v symmetry in the mixed layer, but it shows a strongly altered behavior concerning molecular desorption and dehydrogenation. In particular, a much higher amount of benzene than for the pure layer desorbs molecularly. In the mixed layer, three states of adsorbed NO are formed, with electron accepting species being favored. Characteristic shifts of the N-O stretch frequencies to lower values indicate an enhanced occupation of the antibonding 2π^* orbital of NO which presumably results from indirect charge transfer from benzene to NO through the substrate. During thermal evolution a transformation of NO occupying bridge sites to the terminally bound linear NO^δ+ species is found.