An experimental guided-ion-beam and ab initio study of the ion-molecule gas-phase reactions between Li+ ions and iso-C3H7Cl in their ground electronic state

Reactive collisions between Li+ ions and i-C3H7Cl molecules have been studied in the 0.20-12.00 eV center-of-mass energy range using an octopole radio frequency guided-ion beam apparatus recently developed in our laboratory. At low collision energies, dehydrohalogenation reactions giving rise to Li(C3H6)(+) and Li(HCl)(+) are the main reaction channels, while at higher ones C3H7+ and C2H3+ become dominant, all their reactive cross sections having been measured as a function of the collision energy. To obtain information about the potential energy surfaces (PESs) on which the reactive processes take place, ab initio calculations at the MP2 level have been performed. For dehydrohalogenations, the reactive ground singlet PES shows ion-molecule adduct formation in both the reactant and product sides of the surface. Following the minimum energy path connecting both minima, an unstable intermediate and the corresponding barriers, both lying below the reactant's energy, have been characterized. The entrance channel ion-molecule adduct is also involved in the formation of C3H7+, which then generates C2H3+ via an CH4 unimolecular elimination. A qualitative interpretation of the experimental results based on ab initio calculations is also included. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168332]