Harper, S.M.; (2005) A study of the formation, dissociation and reactivity of molecular dications. Doctoral thesis , University of London.

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Abstract

This thesis describes the commissioning of a new position-sensitive coincidence (PSCO) time-of-flight (TOF) mass spectrometer, which has been designed and constructed for studying the dynamics and kinematics of dication-neutral reactions at low collision energies (4-25 eV). These reactions commonly form two singly charged ions that the PSCO experiment detects in coincidence on an event-by-event basis, allowing definitive partner ion associations to be made. Flight time and positional data are recorded for each ion allowing the calculation of their initial velocity vectors from which the complete dynamics and kinematics for each reactive event, including determination of reactant and product states, may be determined. The "simple" Ar2+-He collision system was investigated for the purposes of commissioning and quantifying the energy resolution of the new PSCO experiment, since it has been previously studied in the literature. Following the successful commissioning of the PSCO experiment, three more complex systems were studied: Ne2+-Ar, Ne2+-N2, CF22+-H 2O, in order to obtain an in-depth understanding of the dynamics and energetics of dication-neutral reactions. The PSCO investigation of the 2_ _ , electron transfer reaction in the Ne-Ar collision system revealed bimodal angular distributions of both products, Ne+ and Ar+, indicating the presence of two different electron transfer channels. The extraction of such detailed information for a simple "two-body" reaction (a reaction where two products are formed) shows that the PSCO experiment is a powerful tool for determining detailed dication-neutral reaction mechanisms. The Ne-N2 collision system indicated the presence of three reaction channels forming Ne+ + N+ + N in coincidence. Two of these channels were investigated revealing distinctly different mechanistic pathways. One channel involves the formation of a transitory collision complex, and the other appears consistent with a sequential process involving the fast dissociation of N2+*. Five reaction channels were observed for the CF22+-H2O collision system: three electron transfer channels and two bond-forming channels including a previously unobserved hydride transfer reaction.

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