Experimental cross-sections energy dependence and an ab initio electronic structure survey of the ground singlet potential surface for reactive Li+ + n-C3H7Cl collisions at low energies

Abstract

Reactive collisions between n-C₃H₇Cl molecules and lithium ions both in their ground electronic state have been studied in the 0.05–7.00 eV center of mass energy range using an octopole radio frequency guided-ion beam apparatus developed in our laboratory and recently modified. At low collision energies, dehydrohalogenation reactions leading to Li(C₃H₆)⁺ and Li(HCl)⁺ are the main reaction channels, while on increasing energies C₃H₇⁺ and C₂H₃⁺ formation become dominant. Cross section energy dependences in arbitrary units for all these reactions have been measured. Also, ab initio electronic structure calculations at the MP2 level have been performed to obtain information about the potential energy surface on which the reactive processes take place. The reactants’ entrance channel leads to the formation of a stable [Li–n-C₃H₇Cl]⁺ ion–molecule adduct that, following an intrinsic-reaction-coordinate pathway and surmounting a transition state, isomerizes to [Li–i-C₃H₇Cl]⁺. From this second minimum, dehydrohalogenation reactions for both n-C₃H₇Cl and i-C₃H₇Cl share a common reaction pathway leading to the same products. All potential barriers explored by reactions always lie below the reactants’ energy. The entrance reaction channel [Li–n-C₃H₇Cl]⁺ adduct also leads adiabatically to C₃H₇⁺ formation which, on increasing collision energy generates C₂H₃⁺via a unimolecular decomposition. A qualitative interpretation of the experimental results based on our ab initio calculations is also given.