SURFACE-ENHANCED RAMAN-SCATTERING OF ORTHO-MERCAPTOBENZOIC ACID IN SILVER SOL

Surface-enhanced Raman scattering of o-mercaptobenzoic acid (OMBA) in silver sol was investigated. At neutral and basic pH OMBA adsorbed dissociatively on the silver surface via both its sulphur and the carboxylate group and existed as sulphidobenzoate. As the sol solution was acidified, the carboxylate group in o-sulphidobenzoate was protonated on the silver surface while the thiolate group was present as a deprotonated ionic form. At pH 1.2, OMBA adsorbed on the silver surface exclusively via its sulphur atom as o-sulphidobenzoic acid. As the bulk concentration of OMBA increased, the effect of favourable surface packing appeared to be more important than the pH effect in determining the surface orientation of adsorbed OMBA.