STRUCTURE DETERMINATION OF AMMONIA ON CU(110) - A LOW-SYMMETRY ADSORPTION SITE

The local adsorption structure of ammonia on Cu(110) has been determin ed in a quantitative fashion using N 1 s scanned-energy mode photoelec tron diffraction. While inversion of the photoelectron diffraction spe ctra using a direct method indicates that the adsorbed NH, molecules a re near to atop sites, a fuller multiple scattering analysis shows tha t the molecule is actually displaced 0.37 Angstrom off the atop site i n a [100] azimuth. The result is ascribed to adsorbate-adsorbate inter actions (steric hindrance) similar to those found in (2 x 1)-CO (pmg) structures seen on several fee (110) surfaces, although in the case of ammonia, it occurs at coverages well below saturation, implying that adsorbate-adsorbate attraction also occurs. These general conclusions are entirely consistent with those of a recent ESDIAD study of this sy stem. (C) 1997 Elsevier Science B.V.