The Adsorbate-Induced Lifting of the Pt(100) Surface Reconstruction - Iras Investigations

Infrared spectroscopy has been used to study CO adsorption on both the reconstructed (hex) and unreconstructed (1x1) surfaces of Pt{100} at 300 K. On the (1x1) surface CO adsorbs on both bridge and on-top sites giving bands at 1864 and 2062 cm-1, respectively. At a coverage of theta = 0.5 a (square-root 2 x square-root 2)R45-degrees overlayer structure is formed. On the (hex) surface, initially only linear CO is observed at 2083 cm-1. High resolution spectra (1 cm-1) show that with increasing exposure a second linear C-O band is observed starting as a high frequency shoulder at 2087 cm-1. At a coverage of theta = 0.5 this new band is accompanied by a very weak bridge band at 1863 cm-1 and dominates the spectrum, the intensity of the original CO peak having diminished to zero. Isotopic dilution measurements show that the two linear C-O bands result from CO adsorption initially on the (hex) phase and then on (1x1) islands created as the reconstruction is lifted. The results are compared with those for NO adsorption on Pt{100}.