Spectral correlation in the adsorption of aliphatic mercaptans on silver and gold surfaces: Raman spectroscopic and computational study

Spectral shifts of the nu(CS) vibrations of several aliphatic mercaptans adsorbed on the Ag and Au electrode surfaces were measured with the surface-enhanced Raman scattering. influence of the chemisorption mechanism on the spectral shift was investigated through ab initio quantum mechanical calculation for CH3SH, CH3S-, CH3SNa, and CH3SMn (M = Ag, Au and n = 1-3). It was found that even though the 2e molecular orbital of methanethiolate makes the major contribution to its chemisorption, the 3a(1) orbital is mainly responsible for the nu(CS) spectral shift. Adsorption of thiolates on the roughened Ag electrode surface seems to occur at the multiple sites such as the three-fold hollow sites while the number of the surface Au atoms interacting effectively with thiolates seems to be less than that of the Ag atoms. (C) 1999 Elsevier Science B.V. All rights reserved.