Surface‐Enhanced Raman scattering spectra of aqueous silver borohydride sols of pyridine and deuterium‐containing pyridines

Surface‐enhanced Raman scattering spectra of aqueous silver horohydride sols of pyridine, pyridine‐4‐d, pyridine‐2,6‐d2 and pyridine‐3,5‐d2 are reported. Depolarization ratios are given as a function of pyridine concentration for a number of pyridine bands over a substantial range of concentrations. Evidence is presented of multiple site adsorption and a new interpretation of these Raman spectra is proposed. The evidence indicates that the surface enhancement derives essentially from the presence of long linear segments of chains of silver spheres in the aggregating sols. The concentration dependence of the depolarization ratios and of the average silver sol particle size show that the depolarization ratio characterizes the extent of dendritic growth of sol aggregates and is thus the same for every Raman band in a given preparation at the same time in the history of its evolution, independent of the rotational characteristics of the sol particles or of the adsorbed pyridine molecules.