EXPERIMENTAL-EVIDENCE FOR THE FORMATION OF FULLERENES BY COLLISIONAL HEATING OF CARBON RINGS IN THE GAS-PHASE

THE discovery1-6 of the spherical carbon cage compound buckminsterfull erene (C60) and the recent development of methods to produce it in bul k7 have led to an explosion in research in the physical and chemical p roperties of this unique species8,9. Nevertheless, the question of the formation mechanism of C60 (or of the other fullerenes) is still far from settled. We have shown elsewhere that carbon clusters in the gas phase develop from linear chains to planar ring systems to fullerenes as their size increases. One can easily envisage the transformation fr om chains to rings, but how the three-dimensional near-spherical fulle renes evolve from large planar rings is not obvious. Here we show that 'heating' these large ring systems above their 'melting' point leads to 100% fullerene formation accompanied by the evaporation of a small carbon fragment (C1 or C3 for odd systems and C2 for even systems). We propose a mechanism, based on these data, for efficient C60 productio n in carbon arcs.