A simple method for determination of orientation of adsorbed organics of low symmetry using surface-enhanced Raman scattering

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.