ROLE OF SP(3) CARBON AND 7-MEMBERED RINGS IN FULLERENE ANNEALING AND FRAGMENTATION

WHEN fullerenes1,2 are fragmented by laser irradiation, they lose C2 fragments and retain a closed carbon cage3. The detailed mechanism of this process remains unknown, although survival of the cage implies that annealing (rearrangement of the bonding) must play an important role3,4. Here we use ab initio quantum-chemical calculations to show that fullerene annealing happens more readily than fragmentation, and that both are intimately related. Our findings imply that the assumptions commonly made about fullerenes5-that they are composed of five- and six-membered rings of sp2 carbons- are not valid under high-energy conditions. In particular, the appearance of sp3 carbon and seven-membered rings is central in both the annealing and fragmentation processes. Our theoretical predictions imply that the high-energy processes of fullerene growth6-11 and coalescence12 are much richer than previously thought, and that their mechanisms may also involve structures containing sp3 carbon and seven-membered rings. Our results may aid in the design of experimental methods for controlling the nature of fullerene cages (for example, doping, opening and re-closing them).