A SURFACE ENHANCED RAMAN-SCATTERING INVESTIGATION OF INTERFACIAL STRUCTURE AT AG ELECTRODES IN ELECTROLYTE-SOLUTIONS OF THE ISOMERS OF BUTANOL

Surface enhanced Raman scattering has been used to study the interfacial solvent structure of three of the isomers of butanol, 1-butanol, 2-butanol, and 2-methyl-1-propanol (isobutyl alcohol), at Ag electrodes in butanol electrolyte solutions. These alcohols interact with the Ag electrode through the O atom. Orientational information is obtained for these solvents by monitoring the nu(C-C), nu(C-O), nu(C-H), nu(Ag-Br), and nu(O-H) regions of the SERS spectra as a function of electrode potential. The alcohol orientations appear to be driven by both the O lone pair and alkane chain interactions with the electrode surface. At positive potentials, 1-butanol is largely parallel to the Ag surface. The alkane end of this alcohol is repelled from the electrode as more negative potentials are applied. The O interaction of 2-butanol at the electrode surface is similar to that for 1-butanol. Additionally, the ethyl unit of 2-butanol is driven away from the electrode surface at negative potentials. Only one orientation is observed for 2-methyl-1-propanol as a function of potential. Again, the interaction of the O with the surface is similar to that of the other two isomers. Interfacial water, existing as a trace impurity in these nonaqueous environments, was also monitored and found to exhibit interesting potential-dependent behavior at these electrodes that might be a useful indicator of the potential of zero charge.