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Science 5 March 1993:
Vol. 259. no. 5100, pp. 1428 - 1430
DOI: 10.1126/science.259.5100.1428
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Articles

Stable Compounds of Helium and Neon: He@C60 and Ne@C60

Martin Saunders 1, Hugo A. Jiménez-Vázquez 1, R. James Cross 1, and Robert J. Poreda 2

1 Department of Chemistry, Yale University, New Haven, CT 06511
2 Department of Geology, University of Rochester, Rochester, NY 14627

It is demonstrated that fullerenes, prepared via the standard method (an arc between graphite electrodes in a partial pressure of helium), on heating to high temperatures release 4He and 3He. The amount corresponds to one 4He for every 880,000 fullerene molecules. The 3He/4He isotopic ratio is that of tank helium rather than that of atmospheric helium. These results convincingly show that the helium is inside and that there is no exchange with the atmosphere. The amount found corresponds with a prediction from a simple model based on the expected volume of the cavity. In addition, the temperature dependence for the release of helium implies a barrier about 80 kilocalories per mole. This is much lower than the barrier expected from theory for helium passing through one of the rings in the intact structure. Amechanism involving reversibly breaking one or more bonds to temporarily open a "window" in the cage is proposed. A predicted consequence of this mechanism is the incorporation of other gases while the "window" is open. This was demonstrated through the incorporation of 3He and neon by heating fullerene in their presence.

Submitted on December 9, 1992
Accepted on January 28, 1993


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes.
L. Becker, R. J. Poreda, A. G. Hunt, T. E. Bunch, and M. Rampino (2001)
Science 291, 1530-1533
   Abstract »    Full Text »    PDF »
Theoretical Evidence for a C60 "Window" Mechanism.
R. L. Murry and G. E. Scuseria (1994)
Science 263, 791-793
   Abstract »    PDF »
Fullerenes: An extraterrestrial carbon carrier phase for noble gases.
L. Becker, R. J. Poreda, and T. E. Bunch (2000)
PNAS 97, 2979-2983
   Abstract »    Full Text »    PDF »


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