Evidence for orientational tunneling of CO intercalated in C-60: A nuclear magnetic resonance study

We characterize the low-temperature dynamics of CO intercalated in C-60 using NMR spectroscopy. CO in C-60 is found to be dynamically inhomogeneous below 30 K: The (CO)-C-13 line shapes reflect a dynamic disorder to static disorder transition, with only quantum tunneling among equivalent orientations in a local S-6 symmetry potential remaining. The increased hindrance of the CO motion cannot be reconciled with common expectations of a homogeneous, thermally activated jumplike reorientation process, but is well accounted for in a model of orientational pinning due to asymmetric distortions of the cage potential. (C) 2000 American Institute of Physics. [S0021-9606(00)70837-3].