Lockyear, J.F.; (2011) The gas phase reactivity of doubly–charged ions with neutral species. Doctoral thesis , UCL (University College London).

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Abstract

Doubly charged atomic and molecular species (dications) are potentially influential reactants in many environments, including our Earth’s own ionosphere and ionospheres of planets and moons such as Mars and Titan. However, the dication chemistry of these energized environments is far from understood. This thesis attempts to experimentally and theoretically characterize some dicationic reactions that could occur in such environments. Moreover, astro–chemists have pondered for decades how the polycyclic aromatic hydrocarbons and long chain alkynes thought to exist in the interstellar medium are synthesized. Reactions of dications with neutral molecules have been proposed as one possible mechanism for the formation of these large molecules. In this context, it is important to undertake a systematic experimental study of the reactions of dications with neutrals to discover the products that might be formed. Dication– neutral reaction dynamics are also not fully understood and are often surprising, meriting further study. A position–sensitive coincidence time–of–flight mass spectrometer has been used to probe the reactions of dications, including Ar2+, N22+, C2H22+, SF42+ and O22+, with a variety of neutrals. The experiment exploits the fact that dication reactions often result in a pair of product monocations. These pairs of charged products are detected in coincidence, on an event–by–event basis, allowing the reaction channels to be characterised. The position–sensitive detection provides data from which the reaction dynamics and energetics can be determined. One might anticipate that dication–neutral interactions would predominantly result in electron–transfer at large interspecies separation. However, this thesis presents results proving that the chemistry can be far more diverse, with bond–formation between the reactants competing favourably with the more dominant electron–transfer process.

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