The adsorption of squaric acid and its derived species on silver and gold surfaces studied by SERS

In situ surface-enhanced Raman spectroscopy (SERS) was used to monitor the electrochemical behavior of squaric acid on a gold electrode in aqueous solution, at different pH values. Octahydroxycyclobutane and other intermediates were identified. The formation of the squarate radical anion is suggested. The relative intensities of the bands in the SER spectra, together with the surface selection rules, suggest that different adsorption geometries of squaric acid and its deprotonated species are involved. In the presence of chloride, squaric acid and hydrogeno-squarate adsorb via the carbonyl and hydroxyl groups on the electrode surface, whereas their adsorption on metallic thin films occurs mainly via the carbonyl moieties. The observation of carbon monoxide and hydrocarbon bands confirms the catalytic effect of the metallic surfaces investigated in the decomposition of such oxocarbon species.