Coplanar dissociation of ethylene and benzene by collision with Ar8+

By collision of 120 keV Ar8+ with planar hydrocarbons, ethylene and benzene, dissociation of multiply ionized target molecules was studied, focusing attention on the possibility that all the fragment ions are ejected, or tend to be ejected, in a single plane. The trajectories of fragment ions were determined by position-sensitive time-of-flight measurements and the angular correlation of the initial velocity vectors was compared to the results of a reference non-planar molecule, ethane. To eliminate ambiguity due to the contribution of the residual gases, dissociation of ethylene-d4 and benzene-d6 was also examined. The results indicate that the initial velocity direction of the fragments indeed tends to be confined in a single plane when the target molecules are planar. That is, the angular correlation of fragment ions conserves the information on the molecular structure even for considerably large molecules.