Highly rotational C₆₀ dynamics inside single-walled carbon nanotubes: NMR observations

Rotational dynamics of C₆₀ molecules composing a one-dimensional (1D) linear array inside single-walled carbon nanotubes have been investigated by ¹³C NMR in a temperature range from 4.2 to 300 K. The temperature dependence of the NMR lineshape and spin-lattice relaxation time (T₁) indicate that the encapsulated C₆₀ molecules exhibit a quasi-free-rotation with correlation times of 5–10 ps at 300 K. With decreasing temperature, the large amplitude molecular rotation continues to 30 K with an activation energy of 467 K. It is suggested that the C₆₀ linear array does not undergo an orientational phase transition, which is associated with its 1D nature. Furthermore, no evidence for the polymerization of C₆₀ molecules is found from the ¹³C NMR line shape analysis.