HYDRATION OF PYRIDINE-4-CARBALDEHYDE AT THE SILVER-WATER INTERFACE - A PH-DEPENDENT SURFACE-ENHANCED RAMAN-STUDY

Surface enhanced Raman (SER) spectra of samples in silver sols have be en used to monitor the relative concentration of protonated and neutra l pyridine-4-carbaldehyde (4PCA) on the silver surface, which is shown to depend on the solution pH, At low pH, the relative amount of adsor bed free aldehyde decreases as the molecule becomes hydrated. When the pH value is in the range 5 < pH < 6, most of the aldehyde is protonat ed and consequently the presence of free aldehyde is not shown in the SER spectrum, As the pH increases further, the neutral hydrate becomes the adsorbed species, The identical nature of the SER spectra of 4-PC A and 4-pyridylmethanol at pH 6.45 confirms the complete hydration of surface adsorbed 4-PCA molecules.