Interfacial study of benzenesulfinate chemisorbed on silver

The oxidative stability of self-assembled monolayer (SAM) of thiols on silv er was examined with matrix-assisted laser desorption/ionization (MALDI) ti me-of-flight (TOF) mass spectrometry (MS). A benzenesulfinate (BS) monolaye r on silver was also prepared and investigated with MALDI-TOF-MS and surfac e-enhanced Raman scattering (SERS). The presence of sulfinate, sulfonate, a nd thiosulfonate fragment ions reveals that thiolate monolayers oxidize in the air. The relative abundance of C6H5SO2- and C6H5SO3- species in the mas s spectra of the monolayer with different air-exposure times provides an es timation of the oxidation progress. In the vibrational spectrum, the large red shift of nu (SOO ), combined with the lack of a shift of I;(C-S) upon a dsorption, indicates its bidentate O-coordination. The orientation of the c onfined molecules, based on the Raman surface selection rules, was derived from the preferential enhancement of the different functional groups. The b enzene ring of BS was found almost normal to the metal surface as a result of the intermolecular forces; that geometry excludes the possibility of the K-system of the benzene ring from participating as another binding site. T he SER spectra of BS obtained via a selective etching process confirms thes e observations. (C) 2001 Elsevier Science B.V. All rights reserved.