Assignment of (n,m) Raman and Absorption Spectral Features of Metallic Single-Walled Carbon Nanotubes

The (n,m) spectral features for isolated metallic single walled carbon nanotubes were deduced by examining Raman excitation profiles. Correlation of the radial breathing mode frequency with diameter identifies the (n,m) index of the metallic tube. Observation of the energy of Raman intensity maximum provides experimental values for the optical transitions directly, and allows for model independent estimation of peak splitting and diameter scaling. The results were extrapolated to all metallic nanotubes using a parameterized functional form deduced from the framework of the Tight Binding approximation.