Experimental evidence for the formation of fullerenes by collisional heating of carbon rings in the gas phase

Abstract

THE discovery^1–6 of the spherical carbon cage compound buck-minsterfullerene (C₆₀) and the recent development of methods to produce it in bulk⁷ have led to an explosion in research in the physical and chemical properties of this unique species^8,9. 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 from chains to rings, but how the three-dimensional near-spherical fullerenes 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 production in carbon arcs.