The chemical effect in surface enhanced Raman scattering (SERS) for piperidine adsorbed on a silver electrode

The relative SERS enhancement factors for piperidine on a silver electrode were determined as a function of the incident wavelength and applied potential. The charge transfer effect (G(CT)) on Raman intensity was estimated from these data, The total chemical effect, which is defined as a product of G(CT) and the so-called ''active sites'' effect, amounts to at least 15 for piperidine adsorbed on silver (a system for which ''charge transfer'' is from the adsorbed molecule to the metal). This chemical enhancement factor is very close to that for pyridine adsorbed on silver (''charge transfer'' from the metal to the adsorbed molecule). Thus, the short-range enhancement mechanism can be equally effective for both directions of ''charge transfer''.