Theory of Raman scattering by molecules adsorbed on electrode surfaces

In this work, we provide a simple classical model to explain the enormous intensity enhancement observed for Raman scattering from molecules adsorbed on electrode surfaces. It is proposed that the origin of the intensity enhancement arises from very large changes in the polarizability derivative with respect to a normal coordinate, by virtue of the image field at the admolecule. A qualitative discussion of the role of adsorbed counter ions is presented. We tentatively propose that the dependence of the intensity enhancement on counter ion concentration may be understood in terms of nearest neighbor dipole-dipole stabilization of surface clusters of counter ions with the adsorbate molecule. We also discuss some limitations of the classical model, and propose some further experiments that may lead to clarification of the ideas presented in this work.