What can Coulomb explosions teach us about clusters

Although C/sub 3//sup +/ is considered to be the fundamental building block of the larger carbon clusters, the geometry of this molecule is unknown. Several authors have reported results of ab initio calculations in which the optimized geometry of the ion is deduced, assuming a linear configuration, in agreement with the structure of the neutral C/sub 3/ molecule. We report here the results of a series of measurements exploiting the Coulomb Explosion Method (CEM) to study the geometric structure of the C/sub 3//sup +/ ion. Our results indicate a cyclic structure for this ion. For comparison, measurements were also made of the carbon geometries of small hydrocarbon cations of the form C/sub 3/H/sub n//sup +/ (n = 1-4). Ring structures, of varying rigidities, are observed for all of these except C/sub 3/H/sub 4//sup +/ which exhibits a linear geometry. We also present results for doubly-charged species. 21 refs., 2 figs