Vibration and torsion-facilitated interactions in para- and meta-disubstituted benzenes

Kemp, David J. (2020) Vibration and torsion-facilitated interactions in para- and meta-disubstituted benzenes. PhD thesis, University of Nottingham.

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Abstract

Intramolecular vibrational (energy) redistribution (IVR) has been a point of discussion in monosubstituted and para-disubstituted benzene molecules for some time, with studies drawing comparisons between related molecules in order to understand the factors that influence the rate at which coupling between vibrational and torsional coordinates is seen. The presence of the methyl rotor, such as in para-fluorotoluene, greatly increases the number of available internal energy levels such that the rate of IVR is expected to increase. It has been suggested, however, that the density of states is not the only factor that causes increased rates of coupling, but small differences in quantum numbers, and thus similarity in character between two states, must also be observed for efficient coupling to occur. Further to this, barriers to internal rotation can be shown to directly affect the positions of the rotor levels, with electronic structure differences between molecules also expected to induce additional changes to vibrational or torsional levels. The expected result of this is that these levels may shift further from, or closer to other levels that may efficiently couple to them.

A combination of photoionisation, photoelectron and fluorescence techniques are employed to record electronic spectra via a number of excited intermediates of three molecules: para-fluorotoluene, meta-fluorotoluene and meta-chlorotoluene. Use of these techniques allows one to probe and understand any interactions occurring between levels, mainly in the S1 excited state, although potential interactions in other states can also be unpicked. A number of energetic regions of the S1  S0 transition in pFT are studied, allowing one to deduce how the coupling evolves as a function of energy, as well gaining insight into how the character of the vibrations and torsions involved in these interactions affects the efficiency of the observed interactions. Further to this, low energetic regions of the S1 state for both mFT and mClT are discussed, allowing one to gain gauge the changes in torsion-facilitated interactions as a function of not only energy, but also of electronic and mass related properties.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Wright, Timothy G.
Besley, Nicholas A.
Keywords: Meta-disubstituted benzenes, Para-disubstituted benzenes, Intramolecular vibrational (energy) redistribution, IVR
Subjects: Q Science > QD Chemistry > QD 71 Analytical chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 60810
Depositing User: Kemp, David
Date Deposited: 18 Aug 2020 11:55
Last Modified: 18 Aug 2020 11:55
URI: http://eprints.nottingham.ac.uk/id/eprint/60810

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