AXIAL AND AZIMUTHAL ANGLE DETERMINATION WITH SURFACE-ENHANCED RAMAN-SPECTROSCOPY - THIOPHENOL ON COPPER, SILVER, AND GOLD METAL-SURFACES

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 C2v 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 THETA = 85 and 76-degrees, respectively. The azimuthal angle PHI was found to vary from 32 to 0-degrees 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.