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Science 6 March 1992:
Vol. 255. no. 5049, pp. 1235 - 1238
DOI: 10.1126/science.255.5049.1235
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Articles

C60 Rotation in the Solid State: Dynamics of a Faceted Spherical Top

ROBERT D. JOHNSON 1, COSTANTINO S. YANNONI 1, HARRY C. DORN 1, JESSE R. SALEM 1, and DONALD S. BETHUNE 1

1 IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099

The rotational dynamics of C60 in the solid state have been investigated with carbon-13 nuclear magnetic resonance (13C NMR). The relaxation rate due to chemical shift anisotropy (1/9T1CSA1) was precisely measured from the magnetic field dependence of T1, allowing the molecular reorientational correlation time, tgr, to be determined. At 283 kelvin, tgr = 9.1 picoseconds; with the assumption of diffusional reorientation this implies a rotational diffusion constant D = 1.8 x 1010 per second. This reorientation time is only three times as long as the calculated tgr for free rotation and is shorter than the value measured for C60 in solution (15.5 picoseconds). Below 260 kelvin a second phase with a much longer reorientation time was observed, consistent with recent reports of an orientational phase transition in solid C60. In both phases tgr showed Arrhenius behavior, with apparent activation energies of 1.4 and 4.2 kilocalories per mole for the high-temperature (rotator) and low-temperature (ratchet) phases, respectively. The results parallel those found for adamantane.

Submitted on September 26, 1991
Accepted on November 18, 1991


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