Resonance Models RE

To this group belong several models of very different kinds such as the image model (RE-IE), the charge transfer (RE-CT) model, the electron-hole excitation model (RE-EH), and the Raman reflectivity model (RE-RF). These models have very little in common except that they all lead to enhancements by virtue of a resonance scattering mechanism. The validity of the last statement is not always realized by people, but it will be shown below to hold true. 

One of the earliest models proposed to explain SERS was suggested and developed by Efrima and Metiu and also by King et It is based on the classical theory of Raman 

The simplest presentation of this mechanism starts from an expression which gives the induced dipole /jl in terms of the total field Et operating on it  

Here y denotes a metal response function and the factor 2 was written in order to obtain the form of an image interaction. From Eqs. (4) and (5) one obtains  

Before discussing calculations of y, which is at the core of this mechanism, we show the equivalence of this model to a resonance enhancement mechanism. We take a simple form of the molecular polarizability. 

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