Ball-and-chain dimers from a hot fullerene plasma

The laser desorption of C-k (k = 60 and 70) fullerene is known to produce a broad distribution of cluster sizes strongly peaking around the integer mu ltiples of original fullerene mass. The "exact dimers" (C-n clusters with n = 2k) and species with slightly fewer atoms (n even) have been characteriz ed previously as fully coalesced large single-shell fullerenes and [2 + 2] cycloadducts. Presently, we investigate the species encountered on the high -mass sides of exact dimers, that is, the clusters with n > 2k (n even), us ing high-resolution ion mobility measurements. Specifically, the drift time distributions for C-n(+) and C-n(-) with n = 122-128, 132-136, and 142-146 have been obtained and compared with the results of trajectory calculation s for various trial geometries optimized using the density functional tight binding and semiempirical (AM1) calculations. We find that, besides the no rmal near-spherical fullerenes and [2 + 2] cycloadducts, these species assu me the "ball-and-chain" structures consisting of two fullerene cages (not n ecessarily those of the original material) connected by chains up to eight atoms long. C-122 and C-132 cations and anions also reveal a substantial ab undance of isomers where the C-C unit is sandwiched between the two fullere nes. Taken in conjunction with earlier findings for smaller fullerene dimer s, presently reported results have allowed us to develop a comprehensive mo del for the chemical reactions occurring in the hot fullerene plasma.