Crossed-beam dc slice imaging of chlorine atom reactions with pentane isomers

We present the first in a series of detailed investigations of the reaction of Cl atoms with hydrocarbons in crossed beams. This study focuses on reaction with the pentane isomers n-pentane, isopentane, and neopentane. These crossed-beam ion imaging experiments rely on "universal" 157 nm probe of the pentyl radical product, with dc sliced detection providing the scattering distributions directly. The results for the different target reactants were studied at two collision energies: approximately 5 and approximately 9 kcal/mol. The scattering results are quite similar for all reactants, suggesting that the nature of the abstraction site has surprisingly little influence on the dynamics. The angular distributions are broad with a backscattered peak at low collision energy and a sharp forward peak at high collision energy. The translational energy distributions are strongly coupled to the angular distributions and show, for the forward scattered products, a sharp peak at 80% of the collision energy for all reactants at both collision energies. The sideways-scattered products show the lowest fraction of energy in translation, while the backscattered translational energy distribution peaks at the lowest energy but extends to the highest, showing evidence of coupling of the internal degrees of freedom and the reaction exoergicity, into translation. The results are discussed in view of the extensive literature on related systems.