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Experimental results are provided that correlate the differential interfacial capacitance of electrode surfaces to the pH properties of surface-confined monolayers of molecular bases such as 4-mercaptopyridine and 4-aminothiophenol. In accord with theoretical predictions, the fractional degree of monolayer protonation is shown to be a function of the solution pH and the electrode potential.

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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.