Periodic Resonance Excitation and Intertube Interaction from Quasicontinuous Distributed Helicities in Single-Wall Carbon Nanotubes

Photoselective resonance Raman scattering from laser ablation grown single-wall carbon nanotubes is demonstrated to be consistent with a response from tubes with all geometrically allowed helicities. This information is drawn from an analysis of the resonance scattering by combining ab initio calculations for the mode frequencies with evaluations of the resonance cross sections for isolated tubes. The resonance excitation was found to exhibit an oscillatory behavior. To match the experiments and the calculations, the frequencies obtained from the latter must be up-shifted by 8.5% on the average. This stiffening is ascribed to the tube-tube interaction in the carbon nanotube bundles.