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Theoretical Studies on the ultrafast photodissociation of molecules

Chapman, Emma Louise (2009)
Ph.D. thesis, University of Birmingham.

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Abstract

Ultrafast photodissociation is a fundamental process in nature. In this thesis we present a study of three very different systems which undergo photodissociation on the femtosecond timescale. A major feature of these processes is the often complex topology of the potential energy surfaces due to coupling between the nuclear and electron motion: termed vibronic coupling. A known feature in potential energy surfaces due to vibronic coupling is the conical intersection and these play a role in all three systems studied. In the first study we investigate NH\(_3\), which exhibits an intersection between the ground and first excited state. As a consequence the dissociation occurs on both states. We use two models to study this system, a 2D and a 6D, contrasting greatly in their complexity and ability to describe the whole molecule. Wavepacket dynamics are used to probe the reaction mechanism and to calculate the branching ratio. A detailed investigation of electronic structure theory methods forms a large part of this research. We apply it to the FNO molecule, a system in which there is coupling amongst the states giving rise to certain topological features on the first excited state. These features are both subtle and difficult to reproduce with ab initio methods. We also present a potential fit of this data and implement wavepacket dynamics simulations on the surfaces. A study of Cr(CO)\(_6\) using electronic structure theory is the final system investigated in this work. In contrast to the other systems, Cr(CO)\(_6\) has many low lying excited electronic states and we investigate this system using Complete Active Space Self- Consistent Field (CASSCF) methods. Using a large active space allows us to include all of the states of interest within one calculation.

Type of Work:Ph.D. thesis.
Supervisor(s):Worth, Graham (Graham A.)
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Subjects:QD Chemistry
Institution:University of Birmingham
ID Code:409
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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