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Title: Bimolecular chemical reaction dynamics : a phase comparison
Author: Dunning, Greg
ISNI:       0000 0004 5923 2498
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Studies of the dynamics of chemical reactions reveal a great deal about their mechanisms and the forces that control the chemistry. However, most of these studies have been performed on isolated reactions in the gas-phase, either experimentally or using computational methods. This thesis presents experimental results for the dynamics of both gas and liquid phase reactions. The results are compared in an attempt to understand the effects a solvent has on the course of a chemical reaction. The gas phase experiments focussed on the reactions of Cl atoms with alkenes, in an extension of previous gas-phase dynamical studies of Cl + alkane reactions. The velocity map imaging (VMI) technique was applied to observe the state resolved scattering distributions of the HCI product of the Cl + propene, isobutene and 2,3-dimethyl but-2-ene reactions. The experimental results were compared to trajectory simulations and it is shown that reactions can proceed by direct hydrogen absh·action or an addition-elimination mechanism. The Cl + 2,3-dimethyl but-2-ene reaction has previously been studied in solution and comparison with the gas-phase results presented here provides direct and quantitative evidence about the influence of the solvent on energy release in a reactive system. Solution phase studies involved the reactions of F-atoms with the organic solvents CD2Cb, CD3CN and CH3CN. Computational and experimental studies of the reactions of F+ H2 and F + CH4, and their deuterated isotopologues, have been at the forefront of advances in understanding the classical and quantum mechanical contributions to a chemical reaction. The 266-nm photolysis ofXeF2 was used as a source of fluorine atoms in solution and required characterisation of the photodissociation dynamics on picosecond timescales. The reactions of F-atoms with CD3CN and CD2Cb solvent were studied with the use of time-resolved infra-red (TRIR) and time-resolved ultraviolet-visible (TRUV-Vis) spectroscopy. Efficient energy flow into the vibrational motion of the DF product competes with dissipation of the energy to the solvent bath within a few picoseconds, and bimolecular reaction rate coefficients, DF vibrational level branching ratios and vibrational cooling rates of DF extracted. Results are also presented for the reaction of CN radicals with acetone in chloroform solution. The HCN and 2-oxy-propyl products of the reaction were probed with TRIR spectroscopy, and much of the excess energy of this exothermic reaction is deposited in vibrational modes of both products. Coupling of these vibrational modes to the solvent bath then thermalizes the product on timescales of tens or hundreds of picoseconds. The results from this thesis are combined with previous studies of reactions in the gas and liquid phases to provide a picture of how the solvent can alter the potential energy surface of a reaction. Possible roles of solvent-solute complexes, solvent caging, solvent restructuring to accommodate reactions, and friction associated with the fluxional motion of the solvent bath are discussed
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available