THE ADSORBATE-INDUCED REMOVAL OF THE PT(100) SURFACE RECONSTRUCTION .2. CO

The CO-induced lifting of the pseudo-hexagonal, clean surface reconstruction of Pt{100} has been re-investigated with infrared reflection-absorption spectroscopy (IRAS) and low energy electron diffraction (LEED). In order to remove inconsistencies arising from previous studies, adsorption on both the reconstructed and the metastable unreconstructed surfaces was studied at temperatures between 90 and 300 K. A sequence of ordered overlayers observed for coverages of theta = 0.5 and above on the unreconstructed surface, including the previously unobserved c(5 root 2 X root 2)R45 degrees structure for theta = 0.6, can be interpreted in terms of new structural models involving both atop and bridging CO. During adsorption on the reconstructed surface at 300 K the (hex) <-> (1 x 1) phase transition can be followed using the C-O stretch. in particular, we observe the co-existence of CO adsorbed on (hex) and (1 X 1) regions in a narrow coverage range. The appearance of CO on the (1 X 1) phase is not only accompanied by a small shift in the linear C-O stretch, but also by the development of a bridge band. At temperatures below similar to 250 K, however, the reconstruction is lifted in a significantly different way. These and other results are compared with the corresponding data for NO described in Part 1 of this study.