SURFACE-ENHANCED RAMAN-SPECTRA OF 2-HYDROXYPYRIDINE AND 3-HYDROXYPYRIDINE IN SILVER SOL

Surface-enhanced Raman spectra of 2- and 3-hydroxypyridines in silver hydrosol were studied. It was observed that 2-hydroxylpyridine exists predominantly as a lactam tautomer in the solid state, in solution and also in the surface-adsorbed state. However, 3-hydroxypyridine retain s its enolic form i.e. it exists just as pyridinol under all these con ditions. The large surface enhancement of the in-plane vibrations in b oth cases suggests that the molecules are adsorbed with their planes a lmost normal to the metal surface. The enhancement factors of the prin cipal Raman bands for both the molecules are inversely related to thei r Hammett sigma (sigma(H)) values. The nu(max) of the new bands which appear on the long-wavelength side of the electronic absorption band o f stable Ag sol an addition of the hydroxypyridines also show an inver se relationship with the sigma(H) values of the molecules. These resul ts suggest that a charge-transfer mechanism is involved in surface enh ancement.