Surface-enhanced Raman spectroscopy of silver etched by CrO3H2SO4: Study of adsorbed sulphate

The surface‐enhanced Raman (SER) spectra of sulphate adsorbed on silver were obtained by treating it with a sulphochromic mixture, CrO3H2SO4. When nitrate or pyridine are added to the etching solution, there is evidence that both species can co‐adsorb with sulphate. The analysis of SER bands obtained under different conditions indicates that in some cases sulphate is perhaps physically adsorbed on the surface, preserving its free ion Td symmetry, whereas in others it is chemisorbed, presumably in the form of a bidentate complex having C2ν symmetry. The antisymmetric stretching vibrational mode ν3 of sulphate is very sensitive to the presence of species co‐adsorbed on the surface.