Dynamical low-energy electron diffraction analysis of the structure of nitric oxide on Pt(111)

The adsorption structure of NO on the Pt(1 1 1) surface at low temperature (90-130 K) was studied by dynarriical analysis of low-energy electron diffraction and reflection absorption infrared spectroscopy. Three different 2 x 2 patterns were identified and their experimental intensity vs. voltage curves (I-V curves) were compared with dynamically calculated I-V curves for the models including the tilted (bent) NO geometry. The differences of I-V curves can be recognized by virtue of the wider incident electron energy range than the previous dynamical analysis. The most promising interpretation is that NO occupies three sites sequentially depending on the NO coverage. In this interpretation, NO first adsorbs at the threefold fcc hollow site, next at the atop site and last at the threefold hcp hollow site. The NO saturation coverage is 0.75 ML (1 ML = 1.5 x 10(-15) molecules/cm(2)). The NO species at the atop site is tilted and those at both hollow sites are upright. Our new model agrees well with the recent density functional theory calculation and explains the experimental results better than the previous model, in which NO transits from the bridge site to the atop site with increasing coverage. (C) 2002 Published by Elsevier Science B.V.