Gas phase proton transfer reactions: Energetics and dynamics

The aim of this work is to develop a methodology for obtaining accurate and reliable bond dissociation energies of hydrocarbons important in combustion and atmospheric processes. Guided ion beam techniques are applied to study the dynamics and energetics of translationally driven endoergic proton transfer reactions and competitive threshold collision-induced dissociation of proton bound complexes. This technique measures the gas phase acidity of a molecule relative to a known gas phase acid. The bond dissociation energy is derived from the gas phase acidity measurement by the negative ion thermochemical cycle. Gas phase studies allow determination of the intrinsic molecular properties in the absence of solvent effects. In addition to experimental studies, electronic structure theory has been applied to model the proton transfer reaction surfaces. The competitive threshold collision-induced dissociation method can measure relative gas phase acidities of species that differ in acidity by up to 50 kJ/mol for two very different species. This is an improvement over previous equilibrium and kinetic methods. The unknown acid can be anchored directly between two well-known acids and measured with an estimated uncertainty of +/-3--5 kJ/mol, at the 95% confidence level. When the competitive method is not applicable, endoergic bimolecular proton transfer reactions can be employed to measure the gas phase acidity of the molecule of interest. This method has the advantage of measuring relative gas phase acidities between two dissimilar species differing by as much as 150 kJ/mol. With careful experimental techniques a gas phase acidity can be measured within +/-4--10 kJ/mol, at the 95% confidence level by the bimolecular proton transfer technique.