The experimental results contained in this thesis demonstrate the pow er of time-of-flight mass spectrometry as a means of quantifying the intensity of a given channel of reaction between molecular dications and neutral collision partners. Such experimental data provides important information as to the fundamental dynamics of the reaction mechanism.
Not surprisingly, given the comparatively recent construction of the experimental apparatus, the research is in its infancy and the scope for future work is considerable. A large number of collision systems remain to be investigated, including the and OCS^^ molecular dications with a variety of neutral collision partners. In addition to previously untried collision systems, much of the work undertaken so far indicates further avenues of research. For example, the Cp2^'^/NH3 collision system exhibits bond-forming reactivity [1]. However, the intrinsic characteristics of the bond-forming process display marked differences to those of the other collision systems that exhibit bond-formation. Such behaviour points to a fundamentally different mechanism of the bond-forming reaction. The use of isotopic collision partners has been demonstrated to be a useful probe of the reaction dynamics [2-15]. Therefore, a comparative investigation of the bond-forming reactivity of the analogous CFi^'^/NDa collision system may provide information regarding the bond-forming reaction mechanism exhibited by this collision system.
Another prime candidate for investigation is the CFs^^/HD collision system. Such work would serve two purposes: firstly, the bond-forming reactivity observed in the and the collision systems have many similar characteristics. Therefore, for the sake of completeness, a comparison of the bond-forming reactivity of the CFs^'^/HD and the analogous CFz^^/HD collision systems would provide a further guide to the similarities of the bond-forming reactivity of the CF]^^ and the CFg^^ molecular dications. The second motivation for the investigation of the CFg^^/HD collision system is that the HCFz^/DCFz^ branching ratio, obtained from this study, would provide a strenuous test of the mechanism of bond formation proposed in Chapter 8.
As discussed in Chapter 1, the use of coincidence techniques provides an effective means of determining the value of the kinetic energy released upon the unimolecular dissociation of a molecular dication formed in a repulsive electronic state [16-20]. The same experimental methodology may also be employed to probe the energetics of the reactions between a doubly- charged reactant ion and a neutral collision partner that result in the formation of two singly- charged ions. Using coincidence methods, the kinetic energy released in the reaction is determined
by measuring the difference in the times-of-flight of the two singly-charged ions formed in the reaction. The experimental apparatus is readily converted from time-of-flight mass-spectrometer mode to coincidence mode by simply changing the timing electronics so that the arrival of successive ions at the detector triggers the START/STOP timing signals. As described in Chapter 1, ion-ion coincidence techniques are characterized by the use of a static source field. However, the use of a static source field with our experimental apparatus would only lead to the deflection of the reactant ion beam, thus preventing reaction with the neutral collision partner. Consequently, the extraction of the product ions produced in coincidence may be achieved by using the same pulsed source field as used in TOFMS mode. This demonstrates the versatility of the experimental apparatus used in this investigation of dication reactivity.
Finally, the fitting of a position-sensitive detector to our experimental apparatus would enable the product ion intensities to be measured at a given scattering angle. As demonstrated by the work of Dolejsek et al [21], the angular (scattering) distribution obtained from such an experiment would be of immense use in acquiring additional information pertaining to the dynamics of a given reactive process.
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