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Molecular dynamics of C60·2S8: A 13C NMR study

par Grell, Anne-Sophie ;Masin, Francis ;Céolin, René;Gardette, Marie France;Szwarc, Henri
Référence Physical review. B, Condensed matter, 62, 6, page (3722-3727)
Publication Publié, 2000-08

Article révisé par les pairs

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Résumé :

13C NMR studies of polycrystalline C60·2S8 are reported. At room temperature, the static 13C NMR spectra are similar to the 13C spectrum of polycrystalline C60, which suggests that C60 molecules undergo fast reorientational motion within the solvate lattice as within pure crystalline C60. This observation seems to contradict previous x-ray results that were interpreted in terms of motionless C60 molecules within the solvate lattice; however, it agrees with thermodynamic measurements according to which the enthalpy for the departure of sulfur from the solvate is nearly equal to that of pure sulfur sublimation. The evolution of the shielding tensor as a function of temperature is also reported: it exhibits a steep change near 150 K that corresponds to a slowing down of the C60 rotational motion. Finally, according to the variation of the 13C spin-lattice relaxation time T1 vs temperature, the dynamics of C60 molecules, which consists in jumps between symmetry-equivalent orientations, can be considered as ruled by two activation energies, 15.3 and 24.8 kJ mol-1. ©2000 The American Physical Society.