# Are metal modes mixed with molecular modes during surface enhanced Raman effect?

This question is dedicated to Martin Fleischmann (1927-2012).

When a molecule is adsorbed on a metal surface, the Raman scattering amplitude from the molecule is enhanced. According to Wikipedia, the downconversion rate is sometime enhanced by a factor of $10^{10}-10^{11}$). Also accoding to Wikipedia, the effect has been attributed to electric field enhancement near the metal, but it has also been attributed to chemical sharing of electrons in the molecule and in the metal. The sharing idea means that many delocalized electrons in the metal can downconvert the photon through the adsorbed molecule, leading to enhancement.

There seems to be controversy. So which is it? What causes the Raman enhancement?

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