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 cryst al violet with and without coexistence of halide ions (Cl-, Br-, I-) i n the low-wavenumber region is studied by using a conventional scannin g Raman spectrometer and near-infrared excitation. It is found that th ere exist at least two active Raman modes in the wavenumber region bet ween 200 and 300 cm(-1) for pyridine adsorbed on colloidal silver in t he presence of chloride ions as well as that the halide ions affect al so the ring breathing modes of adsorbed pyridine. Enhancement and shif t 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 t he Ag-Cl stretching vibration whereas a band at about 221 cm(-1) is du e to the surface complex of the adsorbed pyridine. We also found that more than one Raman mode in the low-wavenumber region are simultaneous ly active for adsorbed crystal violet on colloidal silver in the prese nce 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 vi olet.