Raman Study of the Photochemistry of Maleic Acid Adsorbed on the Surface of Colloidal Silver

The surface-enhanced Raman scattering (SERS) spectra of maleic (cis; 2-butaneoic acid) and fumaric (trans; 2-butaneoic acid) acids adsorbed on aqueous silver sol particles are reported. These two acids form two groups of isomers which differ only in the relative positions of the two carboxylate groups. The photochemistry of maleic and fumaric acids adsorbed on the surface of silver colloids is investigated using SERS as a probe. The photochemical studies of these two acids adsorbed on colloidal silver surfaces show that the photoisomerization of maleic to fumaric acid has occurred. We interpret our spectra as indicating that fumaric acid p bounds through a C=C double bond, while maleic acid s bonds through lone pairs on the carboxylate groups.