Dissociation mechanisms of energy‐selected chlorobutane ions: Experiment and theory

Abstract

AbstractThe breakdown diagrams and photoionization efficiency curves of isomeric chlorobutane ions were obtained by energy‐selected molecular ions with the photoelectron–photoion coincidence (PEPICO) technique. The loss of HCl from 1‐ and 2‐chlorobutane molecular ions was found to be fast, and accurate dissociation onsets were determined from the crossover energy in the breakdown diagrams and appropriately corrected for the precursor thermal energy. In spit of the low activation energy, the isochlorobutane molecular ion was found to dissociate slowly near the dissociation limit, the time‐of‐flight distribution having been analyzed in terms of two exponential decay rates. The dissociation reaction involved a large kinetic energy release that pointed to a 1,2‐elimination leading to a stable C4H ion. AB initio calculations indicated that the reaction path involved an H‐atom transfer through a barrier, which is a favorable case for a tunneling model to explain the slow decomposition rate. The kinetic energy release of chlorine radical loss from tert‐chlorobutane was determined as a function of the ion internal energy. At low energies the kinetic energy release was nearly statistical but the dissociation from the excited electronic states resulted in a large and non‐statistical kinetic energy release.