Surface Enhanced Raman Scattering and Normal Coordinate Analysis of 1,10-Phenanthroline Adsorbed on Silver Sols

The surface enhanced Raman scattering of 1,10-phenanthroline adsorbed on silver sol has been obtained and analyzed by using normal mode calculations based on a valence force field suitably determined for this molecule. Evidence has been found for Ag−N bond formation with the silver surface, supporting the validity of a chemisorption process. The experimental and calculated data suggest an adsorbate−substrate interaction with perpendicular or tilted orientation of the molecule with respect to the colloidal surface. The halide anion effect on the SER spectrum improves a charge-transfer enhancement process involving adsorbate and metal electronic states. The results obtained on colloids agree with those detected by measurements performed on silver electrode. The similarity between SERS and normal Raman spectra of the corresponding 1:2 Ag(I)-phenanthroline complex indicates that the molecule is perturbed upon adsorption as well as upon coordination in the argentous complex.