Raman scattering of adsorbed molecules

The excitation energy dependence of the surface enhanced Raman scattering of adsorbed molecules is calculated based on the effective resonance model for a molecule–metal system. As a consequence of the effective resonant Raman process of the adsorbed molecule, a remarkable departure from an ω4 law is obtained near the excitation energies which satisfy the resonant condition. The significance of the substrate metal on the degree of the enhancement is discussed with the use of a result that the position of the effective resonant level is closely connected with that of the Fermi level. A comparison with the recent experimental results on the excitation profiles is also made.