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-l-propanol (isobutyl alcohol), at Ag electrodes in butanol electrolyte solutions. These alcohols interact with the Ag electrode through the 0 atom. Orientational information is obtained for these solvents by monitoring the v(C-C), v(C-O), v(C-H), v(Ag-Br), and v(O-H) regions of the SERS spectra as a function of electrode potential. The alcohol orientations appear to be driven by both the 0 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 0 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-l-propanol as a function of potential. Again, the interaction of the 0 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.