SURFACE-ENHANCED RAMAN-SCATTERING OF HALIDE-IONS, PYRIDINE AND CRYSTAL VIOLET ON COLLOIDAL SILVER WITH NEAR-INFRARED EXCITATION - LOW-WAVE-NUMBER VIBRATIONAL-MODES

Surface-enhanced Raman scattering from halide ions, pyridine and crystal violet with and without coexistence of halide ions (Cl-, Br-, I-) in the low-wavenumber region is studied by using a conventional scanning Raman spectrometer and near-infrared excitation. It is found that there exist at least two active Raman modes in the wavenumber region between 200 and 300 cm(-1) for pyridine adsorbed on colloidal silver in the presence of chloride ions as well as that the halide ions affect also the ring breathing modes of adsorbed pyridine. Enhancement and shift in band positions of the ring breathing modes decrease in the order Cl- > Br- > I-. The observed band at about 240 cm(-1) is assigned to the Ag-Cl stretching vibration whereas a band at about 221 cm(-1) is due to the surface complex of the adsorbed pyridine. We also found that more than one Raman mode in the low-wavenumber region are simultaneously active for adsorbed crystal violet on colloidal silver in the presence of chloride ions. The experimental results indicate that the Ag-Cl stretching vibration accounts for the Raman band at about 240 cm(-1) and that the Raman mode at about 210 cm(-1) is specific for crystal violet.