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Title: Photofragment Translational Spectroscopy of Heteroaromatic Molecules
Author: Devine, Adam L.
ISNI:       0000 0001 3422 9688
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2007
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This thesis presents detailed studies of the dynamics of H atom loss following UV photoexcitation of several different aromatic molecules containing heteroatom(X)H bonds, performed using the H Rydberg atom photofragment translational spectroscopy (PTS) technique. The fragmentation dynamics of imidazole have been studied following excitation at many wavelengths in the range 210 S; Aphot :5 240 nm. Long wavelength excitation within this range results in the direct population of the dissociative l IA'ctnO'*) excited state, but 21A' ~ XIA'(n* ~ 1t) absorption is shown to become important at ~ :::;; 220 nm. N-H bond dissociation on the 11t0'* surface is rapid and leads to the formation of imidazolyl radicals in their ground electronic state in . selected (low energy) vibrational levels and H atoms with high kinetic energies, generating structured H atom time-of-flight spectra. Studies of photo-induced H atom loss in para-fluorophenol, para-chlorophenol and the three isomers of methyl-phenol, following photolysis at many wavelengths in the range 216 :::;; Aphot :::;; 290 nm, are also reported. These studies reveal that, in each case, excitation is dominated by absorption to a bound 11tn* state. Dissociation proceeds by coupling to the Sl1tO'*) surface, leading to the production ofH atoms and radical products in specific vibrational levels oftheir respective ground electronic states. o Finally, results of an H atom PTS study of thiophenol are presented, in which a dissociative state of InO'* character is likewise shown to play an important role in the non-radiative decay of excited state thiophenol molecules formed on UV excitation. The H atom TKER spectra obtained are highly structured due to the formation of thiophenoxyl radicals in both their ground and first excited electronic states - again in only a very limited subset of the available vibrational state density. In each case, analysis of the vibrational energy disposals in the radicals formed on X-H bond fission following population of electronic states of 11tO'* character is shown to offer uniquely detailed insights into both the nature of the initial parent excitation and of the dynamics of the subsequent bond fission process - particularly the role of the one (or more) conical intersections involved in the evolution from excited parent molecule to the radical product.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available