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Molecular dynamics and photoionisation processes: from strong-fields to soft X-rays

Forbes, Ruaridh; (2018) Molecular dynamics and photoionisation processes: from strong-fields to soft X-rays. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis comprises of a set of time and energy-resolved photoelectron spectroscopy studies of polyatomic molecules exposed to radiation ranging from the IR to soft X-ray region of the spectrum. Chapter 1 provides an introduction to molecular photochemistry, wavepacket dynamics and ionisation mechanism ranging from weak single photon ionisation to strong-field ionisation in intense laser fields. In Chapter 2 an experiment to probe excited state wavepacket dynamics in the molecule NO2 is presented. This experiment is based on using the channel-resolved above-threshold ionisation technique as a multi-dimensional probe of nonadiabatic dynamics in polayatomics molecules. The complex roles of one-photon excitation, multiphoton excitation to higher-lying neutral states, multi-channel neutral and ionic dissociation are examined and complications of using strong-fields to probe photochemistry are outlined. Chapter 3 deals with a VUV/UV time-resolved photoelectron velocity map imaging (VMI) study of Rydberg-valence mixing in high-lying excited states of acetone (CH3-CO-CH3). Details are provided of the implementation of a high-flux femtosecond VUV source based on non-collinear four-wave mixing. The VMI results show evidence of non-adiabatic evolution from the initially prepared 3dyz electronic state to the lower-lying 3p/3s states and subsequent relaxation of these Rydberg states to the pipi* electronic state on a few hundred femtosecond timescale. Chapters 4 and 5 deal with energy-resolved synchrotron radiation studies of the core-level ionisation, excitation and Auger decay in CH3I. Detailed assignments and analysis of the angular distributions connected with the I 4s, 4p and 3d orbitals are provided. These studies are a necessary precursor to aid in the interpretation of time-resolved data obtained using recently developed laboratory and facility based soft X-ray sources. Finally, Chapter 6 provides a summary of the different opportunities offered by performing time-resolved photoelectron spectroscopy in various wavelength regimes and provides an outlook for future work utilising novel ultrafast light sources.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Molecular dynamics and photoionisation processes: from strong-fields to soft X-rays
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2018. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10064651
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