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Title: Intramolecular dynamics in small aromatic molecules : vibrational redistribution and the application of photoelectron angular distributions
Author: Midgley, Jonathan Peter
ISNI:       0000 0004 6351 9504
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2014
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Photochemistry and photophysics are prominent and important phenomena, being involved in such diverse processes as photosynthesis, vision and solar energy capture. An understand› ing of the mechanisms of energy flow after photoexcitation is integral to the reproduction or control of these processes. Such dynamical considerations are intimately related to spec› troscopy - the study of the interaction of light with matter - and by their nature must be treated using quantum mechanical methods. This work aims to build on the current understanding of, and the methods of monitor› ing , photo-initiated dynamics within individual gas-phase aromatic molecules. Multiphoton ionisation and valence photoelectron spectroscopy are used to excite and probe gas phase molecules that have been cooled by means of a supersonic expansion. A time-resolved ap› proach is employed in order to study the process of vibrational redistribution in electronically excited states; dynamics are initiated by a laser pulse of picosecond duration, and a second ionisation pulse, arriving a variable time delay later, is used to probe the changing state of the molecule. The vibrational state of the molecule is indicated by the energy distribution of the photoelectrons, which is measured using the velocity map imaging (VMI) technique. There is the possibility of resolving peaks corresponding to individual ionic vibrational states due to the relatively narrow bandwidth of the laser pulses. Observations are made of os› cillatory dynamics at a number of different energies in the first electronically excited state of para-difluorobenzene. Analysis reveals previously unobserved vibrational structure and sheds further light on the mechanisms of vibrational redistribution . These observations are compared and contrasted with those from fluorobenzene, toluene and para-fluorotoluene in order to investigate the effect of reducing symmetry and the presence of different functional groups on the observed dynamics. The angular distribution of the photoelectrons is also recorded as part of a VMI measurement. These distributions are determined by interference the between the partial waves that describe the wavefunctions of the outgoing electrons, and can be sensitive to the quantum states and alignment of molecules. The potential for using measurements of photoelectron angular distributions (PADs) to monitor intramolecular dynamics is evaluated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available