A MULTIPLICITY OF CN BONDING CONFIGURATIONS ON NI(110)

High-resolution electron energy-loss spectroscopy (HREELS) has been ap plied to CN overlayers created by the dissociation of C2N2 on Ni(110). For the well-ordered overlayer formed at room temperature, the lowest CN stretch frequency (190 meV) so far reported is observed, along wit h distinct frustrated translation and rotation modes. The CN is conclu ded to be lying in the grooves of the surface with both vertical and l ateral pi-bonding. When condensed cyanogen is warmed to room temperatu re, a denser, disordered CN overlayer is formed. HREELS indicates that in addition to the flat-lying in-groove species, CN is adsorbed on th e Ni ridges in both carbon- and nitrogen-bound vertical configurations , as evidenced by a band of very high CN stretch frequencies (245-270 meV) and their associated metal-molecule modes. (C) 1997 Elsevier Scie nce B.V.