NEW DEVELOPMENTS IN ELECTROCHEMICAL INFRARED-SPECTROSCOPY - ADLAYER STRUCTURES OF CARBON-MONOXIDE ON MONOCRYSTALLINE METAL-ELECTRODES

Coverage- and electrode potential-dependent infrared spectra for carbon monoxide on low-index platinum- and rhodium-aqueous interfaces are examined alongside related data for the corresponding metal-uhv interfaces in order to compare the CO adlayer structures in these two types of surface environment. Broadly speaking, the electrochemical systems display a greater propensity for bridging versus terminal CO coordination, especially at the lowest electrode potentials and smallest coverages. These findings can be understood largely in terms of the differences in surface potential between the electrochemical and uhv systems together with the influence of water and/or hydrogen coadsorption in the former case. The formation of extensive CO domains ("islands") during adlayer electrooxidation, which are largely absent during CO adsorption, is deduced from dipole coupling measurements using CO12/CO13 mixtures. The substantial shifts in CO site occupancy in the presence of coadsorbed Bi is also noted. Some implications of the adlayer structures to electrooxidation kinetics are pointed out. The charge-dependent properties of soluble high-nuclearity platinum carbonyl clusters are briefly noted in relation to the behavior of electrosorbed CO.