Carbon cluster cations with up to 84 atoms: structures, formation mechanism, and reactivity

Carbon clusters are generated by laser desorption. Mass-selected beams are then pulse injected into an ion chromatography (IC) device. This device temporally and spatially separates the beam into its isomeric components. Arrival time distributions (ATDs) are then measured at the detector. From these distributions, accurate mobilities are obtained for each isomeric component, along with the the fractional abundance of each isomer. Different isomer structures are calculated using quantum chemical methods. A Monte Carlo technique uses these structures to obtain accurate theoretical mobilities. Comparison of theory with experiment allows unambiguous structural assignment of the various families of isomers present in the cluster beam. The results indicate that, for carbon cluster cations, linear structures exist up to C[sub 10[sup +]]. Several families of planar ring systems begin with monocyclic rings (ring I), which first appear at C[sub 7[sup +]], and persist beyond C[sub 40[sup +]]. Bicyclic rings (ring II) are first observed at C[sub 21[sup +]] and persist beyond C[sub 40[sup +]], followed by tricyclic rings (ring III, initiated at C[sub 30[sup +]]) and tetracyclic rings (ring IV, initiated at C[sub 40[sup +]]). A 3-dimensional family we label as 3-D rings begins at C[sub 29[sup +]], whose structure is not yet unambiguously assigned. This family never exceeds 5% of the ions at any cluster size. Finally, the first fullerene is observed at C[sub 30[sup +]], with this family dominating above C[sub 50[sup +]]. 32 refs., 14 figs., 4 tabs.