Coupling and scattering power exchange between phonon modes observed in surface-enhanced Raman spectra of single-wall carbon nanotubes on silver colloidal clusters

In the surface-enhanced Raman spectra of single-wall carbon nanotubes on silver colloidal clusters, at high excitation laser intensities, we observed with increasing laser excitation intensity, an exchange in the scattering power between two phonon modes that constitute the 1590cm^-1 feature of the G band. We explain this effect in terms of phonon-phonon coupling, which occurs for the extremely strong Raman effect in intense optical fields in the ``hot'' areas of silver clusters.