Identification of Hydroxyl on Ni(111)

Hydroxyl (OH) is identified and characterized on the Ni(111) surface by high-resolution electron energy loss spectroscopy. We find clear evidence of stretching, bending, and translational modes that differ significantly from modes observed for H2O and O on Ni(111). Hydroxyl may be produced from water by two different methods. Annealing of water co-adsorbed with atomic oxygen at 85 K to above 170 K leads to the formation of OH with simultaneous desorption of excess water. Pure water layers treated in the same fashion show no dissociation. However, the exposure of pure water to 20 eV electrons at temperatures below 720 K produces OH in the presence of adsorbed H2O, In combination with temperature-programmed desorption studies, we show that the OH groups recombine between 180 and 240 K to form O and immediately desorbing H2O. The lock of influence of co-adsorbed H2O at 85 K on the O-H stretching mode indicates that OH does not participate in a hydrogen-bonding network.