Trimerization of C-60

Seven different regioisomers of C-60 trimers with intact cages have been ca lculated at the empirical tight-binding total energy calculation method. We analyze the atomic structure and energetics of seven different trimers exc ept the sterically demanding cis-l. The trimers are formed by the linkage t hrough a [2+2] cycloaddition. The energies of the trans-3, trans-1, trans-2 , trans-4, cis-3 and cis-2 regioisomers relative to the most stable equator ial regioisomer are 13, 19, 20, 30, 207 and 673 meV, respectively.