THEORY OF SURFACE ENHANCED RAMAN-SCATTERING IN COLLOIDS

We present a theory of surface enhanced Raman scattering (SERS) that gives a response enhancement of up to ten orders of magnitude for pyridine on silver. The signal obtained depends on the laser frequency and is consistent with available experimental data. Our theory emphasizes the effect of the molecule itself on the polarization of the environment as well as the effect of high multipoles, required by the nonuniformity of the local fields. The host could be metallic or insulating. We explain the laser frequency dependence of the relative size of Raman signals for different vibrational lines and predict the presence of a doublet at each electromagnetic resonance. The effect on the Raman signal of depositing a metallic or an oxide coating over a metallic host is discussed.