Low- and high-frequency intermediate modes with step-like dispersion in resonance Raman scattering of carbon nanotubes.

Resonance Raman spectra of mixture of single-wall carbon nanotubes were investigated in details. The diameter distribution of the investigated nanotubes was estimated from the experimental frequencies of radial breathing modes. Two series of two-phonon lines revealing step-like behavior with excitation energy as well as non-dispersive single-phonon lines were registered in the intermediate frequency range 200-1200 cm(-1). Observed Raman lines were analyzed and their assignment to particular phonons was carried out. Step-like dispersive high intermediate-frequency modes in the range of 720-1000 cm(-1) are attributed to resonance two-phonon processes with combinations of optical and acoustical modes Low intermediate-frequency modes in the range of 300-650 cm(-1), also revealing step-like behavior, are attributed to resonance two-phonon processes with combinations of flexural optical and acoustical modes.