Bartusiak, Marcia F., Burke, Barbara, Chaikin, Andrew, Greenwood, Addison, Heppenheimer, T.A., Hoffman, Michelle, Holzman, David, Maggio, Elizabeth J., Moffat, Anne Simon. "9 Bouncing Balls of Carbon: The Discovery and Promise of Fullerences." A Positron Named Priscilla: Scientific Discovery at the Frontier. Washington, DC: The National Academies Press, 1994.
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A Positron Named Priscilla: Scientific Discovery at the Frontier
fullerene spheres. However, when the IBM researchers prepared their isotope-enriched samples of C70' they found that the 13C was randomly mixed in with the regular carbon atoms. "This implies that the graphite must have been completely atomized before forming fullerenes," said Bethune, "and argues against formation mechanisms that involve tearing multiatom fragments from the graphite."
Surprise: Buckyballs Can't Sit Still
While NMR analysis of C60 in solution allowed researchers to study the molecule's symmetry and bonding, the same kind of analysis done on solid fullerene (referred to as "fullerite") turned out to be a powerful tool for probing the detailed geometry of buckyballs and their properties. And, in fact, solid-state NMR analysis carried out independently by Costantino Yannoni of the IBM group and Robert Tycko at AT&T Bell Labs in Murray Hill, New Jersey, revealed a surprising fact: even when solidified into a crystal (when atoms and molecules normally are locked into place by their neighbors), buckyballs are about as sedate as a five year old in a dentist's chair; they're jittery molecules that don't like to sit still. "At room temperature, they nearly ignore each other," Bethune said, "and spin wildly with no correlation between the orientations of adjacent molecules." Such solids are referred to as "plastic crystals,'' and a few others exist in nature, such as a hydrocarbon called adamantane (C10H16). Its carbon atoms form a tetrahedron-like structure that is studded on the outside with the hydrogen. The sides of the molecule bulge out, giving it a somewhat roundish shape. Adamantane used to be the "classic solid rotator" that held the spin record for plastic crystals until buckyballs came along, said IBM team member Johnson, but the new carbon has clearly broken the record for slipperiness. Even though a buckyball is six times larger, it spins three times faster than adamantane, which is slowed by the hydrogen "bumps" on its surface, Johnson explained.
How fast can buckyballs spin in a solid? The IBM group clocked them at around 20 billion revolutions per second at room temperature and found that this is almost as fast as if the molecules were in gas phase, when there is no hindrance at all to rotation. "That's an incredible rate, pretty wild," said Johnson who added that perhaps buckyballs should be named the "new" classic rotator. Further research at IBM showed that the only way to slow buckyballs is to put them in deep freeze. At 8° F (-13° C), their rotation rate drops abruptly. "That's associated with suddenly the molecules beginning to care about the