How are resonance Raman properties of silver clusters affected by interaction with small molecules?

Raman scattering is caused by the interaction between light and the polarizability componentsof the complex. Over the last few decades, the application of metal nanoparticles, especiallythe ones that support the plasmon excitationshas led to several new more efficientspectroscopic methods including Surface-Enhanced Raman Spectroscopy (SERS).Two majormechanisms were suggestedfor describing the enhancement in SERS; first one is theElectromagnetic Mechanism (EM) as a result of the strong local field at the surface of thenanoparticle which is the main contributionin the enhancement and the second one is theChemical Mechanism (CHEM) due to the chemical coupling between the free molecule andthe nanoparticle. Although it is impossible to separately measure each mechanismsenhancement, it is established that the main contribution is caused by EM.