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Title: The study of ion structures and their reaction chemistry by high-pressure source and collision induced decomposition mass spectrometry
Author: Kelly, L. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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This project has incorporated the use of mass spectrometric techniques to study the nature of protonated species, with respect to structure, thermodynamic properties, and their mechanism of formation. High-energy Collision Induced Decomposition (CID) has been used to probe the behaviour of these species as a function of reaction conditions, with the aim of determining the nature of the protonated species and the interconversion between closely related isomers. Pulsed high-pressure source mass spectrometry (PHPS-ms) has been used to investigate proton transfer equilibria in such systems. A detailed study of seven monoterpenes was undertaken using CID and PHPS-ms, along with semi-empirical theoretical calculations. This combination allowed determination of relative proton affinity data, showing good correlation between experiment and theory. In addition, study of the CI and CID spectra as a function of temperature, with the support of isotope labelling experiments and low-level theory, has given an insight into the most probable sites of protonation of each isomer. The varying CID spectra of these isomers highlight the importance of high-energy CID in studying effects of structural geometry on gas-phase reactivity, and provide evidence for a dependence on ion internal energy for some species. The protonation of ferrocene has been studied by high-energy CID-ms, providing the first experimental evidence for the existence of three protonated structures, ring-, metal-, and agostic “bridge”-protonated structures. Formation of the different protomers was found to be dependent on protonation exothermicity, with the different structures leading to different decompositions indicative of their structure. Finally, an extension to previous studies of protonated benzene was carried out, with the aim of corroborating previous data suggesting a face-centred protonated species. This investigation has shown the original interpretation to be wrong. The protonated benzene turns out to be yet another example of an ion whose CID spectrum is dependent on its internal rotational temperature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available