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Title: Probing molecular structure and dynamics with coherent extreme ultraviolet and X-ray pulses
Author: Squibb, Richard James
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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This thesis presents how sources of coherent sources extreme ultraviolet (XUV) and soft X-ray wavelengths can be generated and how these sources may be used to study both the dynamics and structure of molecular systems. Developmental work on a beam line designed to generate XUV radiation using high harmonic generation is presented. In addition to commissioning experimental work using both a flat-field XUV spectrometer and magnetic bottle electron spectrometer, software development work towards building a scalable and future proof acquisition framework for future experiments is presented. The remainder of the thesis presents results obtained from experiments performed at the Linac Coherent Light Source (LCLS) X-ray free electron laser (FEL). We demonstrate that by using a UV femtosecond pulse and a weakly focused X-ray pulse of duration 70 fs, the evolution of UV induced photoisomerisation of 1-3 cyclohexadiene can be tracked. Over timescales of ≈1 ps after UV excitation, the ion yields of the H+ and C+ species were observed to increase by 10% and the observed kinetic energy of all fragments is observed to increase over the same time scale, which can be explained by the structural change of the molecule into the hexatriene isomers. There has been a recent focus in FEL science in using tightly focused X-rays to generate so called hollow atoms, with a completely empty inner shell. Study of the products of the creation of these states ideally requires a measurement in coincidence of multiple particles. We demonstrate that by using the technique of partial covariance mapping (PCM) in conjunction with a high efficiency electron time-of-flight spectrometer, multiple processes in the core ionisation of neon can be resolved. We also use the scheme to successfully measure single site double-core hole states in the hydrocarbons of acetylene and ethane. We discuss how this technique will be a powerful tool in future experiments designed for chemical analysis of the core hole states of systems.
Supervisor: Frasinski, Leszek Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available