Theoretical Study of the Raman Spectra of C70 Fullerene Carbon Peapods

This work focuses on the hybrid system between C70 and a carbon nanotube (C70 peapod) where the encapsulated C70 peas and the nanotube pod are bonded through van der Waals interactions. The nonresonant Raman spectra of these nanomaterials were calculated in the framework of the bond-polarizability model combined with the spectral moment method. The optimal configurations of C70 molecules are derived using a convenient Lennard-Jones potential. We find that increasing the nanotube diameter leads to three successive configurations: lying, tilted, or standing alignments of C70 molecules along the nanotube axis. The changes of the Raman spectra as a function of the configuration of the C70 molecules inside the nanotubes are identified. The nanotube chirality and diameter effects on the Raman-active modes in peapods with different C70 filling factors are studied. This work provides benchmark theoretical results to understand the experimental Raman spectra of C70 fullerene peapods.