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Title: Probing nonadiabatic dynamics in isolated molecules with ultrafast velocity map imaging
Author: Chatterley, Adam S.
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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Two complementary experiments were used to study the ultrafast dynamics of large molecules in the gas phase. Both experiments used time-resolved pump-probe velocity map imaging to monitor energetically dispersed spectra of isolated systems on a femtosecond timescale. A ‘bottom-up’ methodology is applied, whereby initially simple, small, systems are studied in a high level of detail, and then the complexity of system studied is gradually increased. The overall goal was to explore the concept of photostability, the mechanism whereby molecules can withstand bombardment by visible and ultraviolet light, especially in biomolecules. In the first set of experiments, based in Warwick University, the dissociation of hydrogen atoms from neutral phenol and 2-hydroxy phenol (catechol) following ultraviolet excitation was measured with femtosecond resolution. These experiments give unprecedented insight into the electronic structure of phenolic systems, and in particular hydrogen atom tunnelling underneath a conical intersection was directly observed. Varying the excitation energy allowed the transition from tunnelling dynamics to direct dissociation dynamics to be observed. The second set of experiments, completed at Durham University, performed timeresolved photoelectron spectroscopy on large gaseous anions from an electrospray source. The electrospray technique allows very large ions to be introduced into the gas phase, so the bottom-up methodology can be continued. First, the dynamics of the common dye indigo carmine were explored, demonstrating that excited state proton transfer accounts for its photostability. Secondly, the dynamics of the nucleotides making up DNA were explored. The dynamics of nucleobase chromophores were shown to map onto larger nucleotide and oligonucleotide systems, retaining ultrafast photostable properties. Finally, a new instrument was designed and constructed in Warwick. This machine will use laser desorption techniques to help further extend the size range isolated dynamics can be studied in, this time for neutrals. Overall, the bottom-up methodology grants insight into the excited state dynamics of real-world relevant molecules, at an extremely high level of detail.
Supervisor: Not available Sponsor: Leverhulme Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QP Physiology