Surface Enhanced Raman Spectroscopic Study of 2- and 3-Bromothiophenes in Silver Hydrosol

Abstract

Abstract Surface enhanced Raman spectra (SERS) of 2- and 3-bromothiophene molecules in silver sol are compared with those of molecules in acetonitrile solution. The experimental results suggest that the 2-isomer is adsorbed on the metal surface through both the sulfur and the bromine atoms, with the thiophene molecular plane almost normal to the surface, whereas the 3-isomer is adsorbed principally through the sulfur atom. The Raman excitation profile of the molecules in the surface adsorbed state follows surface plasmon resonance frequency, reflecting the contribution of classical electromagnetic effect to SERS in silver sol. The observed “first layer effect”, i.e. maximum enhancement on a monomolecular layer formation on the metal surface, suggests charge transfer contribution to SERS of these molecules. Further, appearance of Ag–Br and Ag–S stretching modes in the SER spectra of 2-isomer indicates chemisorption of the adsorbate molecules on the metal surface.