VISIBLE RAMAN AND NEAR-INFRARED FOURIER-TRANSFORM RAMAN CHARACTERIZATION OF ADSORBED 4,4'-CYANINE

Raman spectra obtained using several visible excitation wavelengths and a dispersive monochromator and FT-Raman spectra obtained using a CW Nd:YAG laser at 1.064-mu-m (9395 cm-1) and a FTIR spectrometer are combined to gain enhanced detail about the structural character of 4,4'-cyanine adsorbed at various potentials onto a silver electrode from solutions of high and low pH. Spectral information is interpreted to indicate that the most prevalent substituents in the electrode adsorbate are polycrystallite and interfacial aggregate molecules: at high pH, the adsorbate is mainly polycrystalline material, while at low pH, the polycrystalline is solubilized and the aggregate exists in principally its protonated form. Also, for near-IR excitation in the low-pH system, the absolute increase in intensity of Raman bands over that for the high-pH system is interpreted as indicating that aggregation enhancement is a principal enhancement mechanism at both high and low pH.