Multiple adsorbed states and surface enhanced Raman spectra of crotonic and sorbic acids on silver hydrosols

Abstract

Abstract Surface enhanced and ordinary Raman spectra of crotonic and sorbic acids were recorded in the range 100‐2000 cm −1 . The changes in the SERS spectra of the two compounds on silver hydrosols with time are shown. From the spectra, it is deduced that there are at least three adsorbed states for crotonic and sorbic acids on silver hydrosols. An unusual SERS spectrum is observed when the acid‐sol systems are heated at 100°C for several minutes. Only four new bands apper whereas the other bands which occur in the spectra of the unheated systems disappear. This interesting phenomenon can also be observed for acetic, hydroxyacetic and propionic acids. It is suggested that the unusual spectrum could arise form a particular adsorbed state of the carboxylate ions on silver sols but not the surface‐catalysed reactions.