Coherent quasielastic neutron scattering study of the rotational dynamics ofC60in the orientationally disordered phase

Coherent quasielastic neutron scattering has been used to investigate the character of the rotational dynamics in the high-temperature solid phase of ${\mathrm{C}}_{60}$. The observed scattering can be described by a model in which each molecule undergoes rotational diffusion which is uncorrelated with the motions of adjacent molecules. The rotational diffusion constant ${\mathit{D}}_{\mathit{R}}$ is (1.4±0.4)×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ at 260 K and (2.8±0.8)×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ at 520 K. The temperature dependence of ${\mathit{D}}_{\mathit{R}}$ is consistent with a thermally activated process having an activation energy of 35±15 meV.