Stability of buckminsterfullerene and related carbon clusters

Under appropriate collisional conditions the mass spectrum of carbon fragments produced by laser vaporization of graphite is dominated by C/sub 60/ and (to a lesser extent) C/sub 70/ clusters. The discoverers of this phenomenon have noted that the carbon valence requirements can be satisfied in closed, hollow structures. For C/sub 60/ they suggest an icosahedral soccer ball network, which they call buckminsterfullerene and we abbreviate as BF. Experimental support has come from studies with lanthanum-impregnated graphite. The resulting mass spectra show intense C/sub 60/La peaks, but no C/sub n/La/sub 2/ or C/sub n/La/sub 3/ peaks. Subsequent experiments have demonstrated the inertness of C/sub 60/ and, indeed, other large C/sub 2n/ clusters under NO attack. We report here the results of quantum calculations which were prompted by the experiments cited above and other earlier work. Our purpose has been to test the intrinsic stability of BF and related polyhedral species and to compare their stability with that of planar graphite fragments. The latter have the advantage of being strain free, but suffer from dangling valences on their perimeters. We also make comparisons with linear carbon chains.