CHEMISORPTION GEOMETRY OF NO ON RH(111) BY X-RAY PHOTOELECTRON DIFFRACTION

The adlayer structure of (2 x 2)-3NO on Rh(111) has been investigated by high-energy, scanned-angle X-ray photoelectron diffraction (XPD) in conjunction with single scattering cluster theory and R-factor analys is. In addition, a plausible adlayer registry, consistent with previou sly published HREELS data, is deduced by means of physical reasoning. The resulting structural model consists of NO bound to atop, three-fol d hollow fee, and three-fold hollow hcp sites through the N atom with an NO bond length of 1.15 Angstrom. NO molecules at all three sites wi thin the adlayer are oriented normal to the surface. The Z coordinates (Z being defined as perpendicular to the surface) of atop and hollow- site NO molecules relative to the top layer of Rh atoms differ by 0.5 Angstrom, with hollow-site NO being bound more closely to the substrat e. This structure differs considerably from one proposed previously by a LEED I-V analysis in both the site occupancy and the spacing of NO molecules within the adlayer.