The EM Model for SERS

The basic concept of the purely electro-magnetic model considers a Raman active molecule (scatterer) near a metallic particle shown schematically in 

Here and denote the dielectric functions of the metallic sphere and its surrounding, respectively. is a depolarization factor depending solely on particle shape. 

8m((o) = x((o) + i 2( B) IS the exprcssioti for the complex dielectric constant. The maximum of the internal field Ei s occurs at a frequency cOsp, where 

The condition corresponds to the excitation of localized surface plasmons. Silver can satisfy this condition for visible light. 

The expression (7) for is identical to that of the electric field, due to an ideal dipole at the center of the sphere (A. = 1/3) 

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