In Situ Infrared Reflection Absorption Spectroscopy of Aromatic Thiols Adsorbed on Gold Electrodes

In order to acquire spectra of organic materials adsorbed on electrode surfaces by in situ infrared reflection absorption spectroscopy, several new techniques have been developed. The spectra of 2, 5-dihydroxythiophenol (DHT) and p-mercaptophenol (MP) adsorbed on polycrystalline gold electrodes were measured as a function of potential using these new in situ IRRAS techniques.The techniques developed in this work made it possible, in the fingerprint region, to monitor the changes in the vibrational properties of monolayer-adsorbed DHT and MP as a function of the applied potential. The overall spectral characteristics of both DHT and MP and their quinone derivatives in the adsorbed state closely resemble those of their solution-phase counterparts. The relatively high intensity of the signals observed for the adsorbed species provides strong evidence that both DHT and MP are adsorbed on gold with the molecular plane nearly perpendicular to the electrode surface and that their oxidation states change with potential change.