Axial and Azimuthal Angle Determination with Surface-Enhanced Raman Spectroscopy: Thiophenol on Copper, Silver, and Gold Metal Surfaces

Article abstract of DOI:10.1021/j100177a068

Raman spectra of noble-metal phenylthiolates and the corresponding surface-enhanced Raman (SER) spectra of the surface species on copper, silver, and gold are reported.Periodic trends were found in both the bulk Raman spectra of the phenylthiolates and the SER spectra.Intensities of the Raman spectra approach that of liquid thiophenol as the metal changes from copper to silver to gold.The SER spectra were used to obtain orientations of the thiophenol species at the noble-metal surfaces.Orientations were determined through the electric field enhancement of vibrations normal to the metal surface.The model developed in this paper allows one to determine both the azimuthal and axial angles of C_2ν molecules at surfaces.This is possible by performing the SERS measurement in media of differing indexes of refraction.For silver and gold we found the axial angle Θ = 85 and 76 deg, respectively.The azimuthal angle Φ was found to vary from 32 to 0 deg from silver to gold.The SER spectra of copper were too weak for accurate angle determinations with a surrounding media other than air.However, the SER spectrum observed on copper in air does indicate a near-perpendicular orientation.