Inelastic scattering surface active molecules

There is some experimental evidence to indicate that much of the enhancement is associated with surface roughness (local microstructures) in the range of 1 to 100 nm. At resonance with th microparticle modes the local electric field at the incident frequency (h L) becomes large near and on the particle surface. Furthermore, the re-radiation efficiency of Raman active molecules situated near the surface also becomes enhanced when the inelastically scattered frequency (hco,) is also in resonance with these microparticle modes. The Raman scattering intensity of the adsorbed molecule is then given by... 

Fig.4.7. Inelastic scattered intensi-ties lu and ly for arrays of active molecules uniformly distributed over spherical surfaces at radial distances a, 0.166a (-----), 0.5a...

The site specificity of reaction can also be a state-dependent site specificity, that is, molecules incident in different quantum states react more readily at different sites. This has recently been demonstrated by Kroes and co-workers for the Fl2/Cu(100) system [66]. Additionally, we can find reactivity dominated by certain sites, while inelastic collisions leading to changes in the rotational or vibrational states of the scattering molecules occur primarily at other sites. This spatial separation of the active site according to the change of state occurring (dissociation, vibrational excitation etc) is a very surface specific phenomenon. 

N. Felidj, J. Aubard, and G. Levi, Effects ofvarious halide ions and probe molecules on inelastic Mie scattering from SERS active surfaces Determination of particle size distributions from band shapes simulation, J. Chem. Phys. 24, 9735-9746 (1996). 

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