LAYER INTERACTIONS BETWEEN DISSIMILAR ADSORBATES - NH3 LAYERS ON CHEMISORBED CO ON NI(111) - A REFLECTION INFRARED STUDY

Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) has been used to study the adsorption structure of NH3 on top of a saturated CO layer on Ni(III). The IRAS results show that NH3 is adsorbed on top of the saturated CO layer on Ni(III) with its C3-upsilon axis tilted away from the surface normal due to the interaction with underlayer CO molecules. Two types of overlayer NH3 species are observed, with one NH3 species exhibiting strong N-H-OC bonding. At the same time, the population of underlayer CO species (bridged and terminal) on different adsorption sites is strongly modified by the adsorption of NH3 molecules in the top layer, with terminal CO decreasing in coverage and bridged CO increasing in coverage. This is due to the influence of an extra (positive-outward) electric field imposed on the CO layer by the polarized NH3 overlayer.