Surface-Enhanced Raman Scattering as a Ubiquitous Vibrational Probe of Transition-Metal Interfaces: Benzene and Related Chemisorbates on Palladium and Rhodium in Aqueous Solution

Abstract

A recently developed strategy for utilizing surface-enhanced Raman scattering (SERS) to obtain uniquely detailed vibrational information for a myriad of organic (and other) adsorbates on transition metals in electrochemical and other ambient environments is illustrated for benzene and a pair of monosubstituted benzenes, toluene and benzonitrile, on palladium and rhodium films in aqueous solution. The transition-metal layers, formed by constant-current deposition onto SERS-active gold substrates, can be sufficiently thin (3−5 monolayers, ML) so to yield near-optimal Raman scattering intensities, yet are essentially devoid of exposed “pinhole” sites, thereby eliminating spectral interferences from adsorption onto gold. Benzene was selected in view of the detailed vibrational information also available for this archetypical organic chemisorbate on transition metals in ultrahigh vacuum (UHV) by means of electron energy loss spectroscopy (EELS). Comparison of the spectral information obtained by SERS and EELS ...