Investigation of the surface structure of colloidal platinum by infrared spectroscopy of adsorbed CO

The infrared spectra of (CO)-C-12 and of (CO)-C-12-(CO)-C-13 mixtures adsorbed on poly(vinylpyrrolidone)-stabilized colloidal platinum in liquid dispersion are reported. Comparison with the vibrational spectra reported for analogous supported Pt particles shows the absence of detectable terrace sites on the colloidal particles. Spectral features resulting from vibrational coupling between the adsorbed CO molecules are analysed in terms of the structure and sizes of the metal particles and the adsorption sites available for CO.