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Title: Targeting low vapour pressure compounds in gas-phase electron diffraction
Author: Schirlin, Julien T.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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Gas-phase electron diffraction (GED) has remained the most valuable technique for the collection of structural information in the gas phase, for the last 70 years. Unfortunately, this structural technique had reached a limiting factor: the volatility of chemicals.  Therefore this work aims to provide new ways to overcome both the kinetic and thermodynamic aspects of this problem by the adoption of a new nozzle design and by the use of a reservoir. The new nozzle extends the capabilities of gas electron diffraction to compounds with lower vapour pressures or with vaporisation rates not adequate for the existing GED experimental conditions. The shape of the new nozzle allows the user to operate at a lower vapour pressure by increasing the diffraction area. The design investigated is the slit type. It allows the electron beam diameter to be kept small, but permits the gas to emerge from a slit running parallel to the beam. Collected and simulated data have confirmed our intuition that the amplitudes will be affected slightly by the slit nozzle. Superimposing simulated and collected data allowed us to establish the profile of the gaseous output from the new design nozzle and shows that the count of electrons being diffracted increase 5.5 fold, with respect to the conventional nozzle. Gas-phase electron diffraction data have been collected and analysed for 2,5-dichlorothiophene and 3,4­dichloro-1,2,5-thidiazole. An extensive series of ab initio calculations has also been undertaken on these molecules, together with 2,5-difluoro and 3,4-dichlorothiophene, allowing the accurate determination of their gas-phase molecular structures. The structures are compared to those of their parent compounds in order to assess the effects of halogen substitution on the rings.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available