Surface-plasmon-polariton resonance factors in a classical calculation of surface-enhanced Raman scattering

The effect of resonant excitation of surface-plasmon polaritons of a general metal substrate on the relatively long-range classical enhancement of the surface-enhanced Raman scattering is considered. It is shown that all the three factors in the classical enhancement arising from the presence of the metal, namely the local electric field at the molecular site at the incident frequency, the electrodynamic renormalization factor for the molecular polarizability, and the propagator for the Stokes scattered field, are modified resonantly. However, their individual impact on the total enhancement differs appreciably, depending strongly on the shape of the metal surface and the distance of the molecule from the surface. As an example, explicit results are given for a molecule adsorbed on a small sphere.