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A simple method for the determination of the orientation of low-symmetry adsorbates on metal surfaces supporting surface-enhanced Raman scattering by predominantly the electromagnetic mechanism is presented. This method is based on the modification of the isotropic intensity ratio of two vibrational modes of known spatial relation of the molecule by the total electric field, and hence radiation intensity, existing at the metal surface. This total radiation field represents the vector sum of the components normal and tangential to the metal surface, both of which exist for radiation in the visible-wavelength region. The validity of this method is demonstrated for methanol adsorbed on Ag surfaces through the use of the symmetric and asymmetric v(C-H) vibrations. Application of this approach to a series of molecules containing four carbon units and methyl groups (1-butanol, 2-butanol, isobutanol, 1-butanethiol, and 2-butanethiol adsorbed on Ag surfaces and 1-butanethiol adsorbed on Au surfaces) is reported.

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Surface enhanced Raman scattering (SERS) and differential capacitance have been used to study interfacial solvent structure in LiBr electrolyte solutions of three isomers of butanol, butan-1-01, butan-2-01 and 2-methylpropan-1-01, at Au electrodes. The potential-dependent spectral behaviour in the regions containing the v(C-C), v(C-0) and v(C-H) modes of these isomers at Au electrodes is compared to that observed at Ag electrodes as a function of rational potential. Differential capacitance data are treated using the Hurwitz-Parsons analysis to extract surface coverage of specifically adsorbed Bras a function of electrode potential. Potential of zero charge (P.z.c.) values are estimated from these data. Based on a quantitative comparison of spectral data at Ag and Au electrodes as a function of rational potential, the solvent structures at Au electrodes are concluded to resemble those previously proposed for Ag electrodes. The potential-dependent orientations of these solvents appear to be driven by interactions of the 0 non-bonding electrons and the alkyl chain with the electrode, and hydrogen bonding of the hydroxy group with specifically adsorbed Br-. At potentials positive of the P.Z.C. at both metals, butan-1-01 and butan-2-01 hydrogen bond with specifically adsorbed Br-with their alkyl portions relatively close to the electrode surface. As more negative potentials are applied, Br-is repelled from the surface, and the alkyl groups move away from the electrode surface insofar as is possible. Only minor changes in orientation are observed as a function of potential for 2-inethylpropan-1-01 at these electrodes due to the symmetry of its alkyl structure. The interaction of the 0 atom of 2-methylpropan-1-01 with the electrode is similar to that observed for the other butanol isomers. This interaction places the alkyl groups of the molecule at the surface in an orientation which is largely potential-insensitive.Determination of the orientation of solvent molecules and the chemical nature of the interaction of these solvent molecules at metal electrodes is of considerable interest to electrochemists due to the importance of the interfacial molecular structure in influencing heterogeneous electron transfer events. The solvent plays an important role in electrochemical systems through solvation of the electrode surface, supporting electrolyte and electroactive species in the interfacial region. However, very little detailed information at a molecular level is available about solvent molecules within electrochemical interfaces. The paucity of studies in this area is particularly acute for non-aqueous electrochemical systems.Vibrational spectroscopy holds extraordinary promise for the elucidation of such molecular details about electrochemical interfaces. Surface enhanced Raman scattering (SERS), in particular, has been used quite effectively to characterize in situ the identity, structure and orientation of adsorbates in electrochemical interfaces. SERS has also been used to investigate electrode-solvent interactions ...