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Title: Velocity map imaging and other spectrometric studies of molecules and clusters
Author: Zaouris, Dimitrious K.
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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The growing interest in the study of gas phase photodissociation dynamics has led to the development of experimental techniques to aid in the understanding of these processes in small (diatomic or triatomic molecules) and in larger systems. In addition, deposition of molecules on large clusters provides information of the clustering dynamics, which can shed light on the processes taking place in the condensed phase. The experiments described in this thesis use nanosecond and femtosecond velocity map imaging to explore the photo dissociation dynamics of a variety of systems on different timescales, and mass spectrometry to investigate the pick-up dynamics of several molecules on clusters. The experiments described in Chapter 3 concern iodine atom loss following the UV dissociation of iodocyclohexane. The bimodal kinetic energy distributions observed are attributed to the dissociation of axial and equatorial conformers of this molecule. The experimental results were complemented by ab initio calculations and two impulsive models. The results were also compared to the dissociation of CH3I, which is generally considered a benchmark system in the field of photodissociation dynamics. In Chapter 4 a time-resolved investigation of the photophysics of electronically excited chlorophenols is presented. The results emphasise the effect of intramolecular hydrogen bonding. To validate these results, the excited state decay of phenol has also been studied and used as a benchmark, since its dynamics have been studied in more detail. Furthermore, there is an introduction to on going high accuracy ab initio calculations, which aim to investigate the various conical intersections by which the electronically excited molecules can transfer to lower electronic states. Chapter 5 presents the experimentally determined pick-up cross-sections of several molecules (NO, HC1, etc) on ice nanoparticles. Particular emphasis is devoted to the pick-up of water molecules by large water clusters. For this process MD simulations have also been carried out. The experimental and theoretical results have been compared to the geometrical cross-sections, which are widely used in atmospheric models. The differences are discussed and the conclusions suggest that the (larger) experimentally determined cross-sections should be used in atmospheric models. Finally, Chapter 6 is dedicated to the recent upgrades of the Bristol VMI spectrometer. The spectrometer was fitted with new ion optics, for which the design details, the simulations and the results from experimental testing are presented. In general the new ion optics design performs better than the one used till now, giving better velocity resolution. However, the final resolution achieved thus far is limited 'by factors other than the configuration of the assembly. These factors are investigated and an effort is made to quantify their effect on the achievable resolution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available