Surface Enhanced Raman field enhancement Theory

In this paper, we report on simultaneous consideration of incident field enhancement and local density of photon states enhancement near a metal particle with spherical shape as a reasonable primary model for single molecule Raman spectroscopy. Joint action of these two factors at the same point of space is found to offer up to lO -fold enhancement of Raman scattering rate. To the best of our knowledge this is the first evidence that consistent theory of single molecule Raman spectroscopy and comprehensive description of so-called hot points in surface enhanced spectroscopies can be constructed without necessarily involvement of chemical mechanisms. 

The central problem in understanding the chemical contribution to the overall enhancement reduces to the calculation of the polarizability of the adsorbate metal surface complex. The mixing of molecular states with metal states may bring about a large effective polarizability. The polarizability a depends on the normal mode amplitude of the molecular vibration Q. In the image field theory of SERS the effective polarizability aeff(Q) depends on the distance between the point molecule and the metal surface and on and e . In order to obtain Raman enhancement the distance between molecule and metal is in the range of 1.5 to 4 A. 

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