STRUCTURES AND ENERGIES OF SMALL CARBON CLUSTERS - WHAT EXPERIMENT AND THEORY HAVE TO SAY ABOUT C-8(+), C-9(+) AND C-10(+)

The structure and energetics of linear and monocyclic carbon duster cations C-n(+) (8 less than or equal to n less than or equal to 10) have been investigated using gas phase ion chromatography experiments and ab initio calculations. Cluster ions are either produced directly in the ion source by laser ablation of graphite or by collision induced dissociation of larger clusters. The relative amount of linear and cyclic isomer was determined as a function of injection energy in the drift cell. Both linear and cyclic clusters are observed at all injection energies. Using simple kinetic arguments, the cyclic isomer is shown to be lower in energy than the linear cluster ion for n = 8,9 and 10. The stability of the cyclic ion relative to the linear isomer is estimated to be 23 +/- 8 kcal mol(-1) for C-8(+), 17 +/- 8 kcal mol(-1) for C-9(+) and 47 +/- 8 kcal mol(-1) for C-10(+). Restricted open shell ab initio calculations are in very good agreement with these numbers.