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

The structure and energetics of linear and monocyclic carbon duster ca tions 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 t he ion source by laser ablation of graphite or by collision induced di ssociation of larger clusters. The relative amount of linear and cycli c isomer was determined as a function of injection energy in the drift cell. Both linear and cyclic clusters are observed at all injection e nergies. 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. Th e stability of the cyclic ion relative to the linear isomer is estimat ed 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.