Generation and structural characterisation of transient gaseous species.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Gas electron diffraction (GED) is a technique that has been developed to study the molecular structure of species in the gas phase. This thesis focuses on the reconstruction of the Canterbury GED apparatus (moved from Edinburgh, UK) and the requirements for modifying the apparatus to incorporate a mass spectrometer (MS) so diffraction and MS data can be obtained within a single experiment.
The combined GED-MS system has been identified in previous work in the Masters group as a necessary development for studying the structure of short-lived species generated in situ. This is particularly true for the study of ketene, which as shown in this thesis, can be generated from several precursors as part of a multiple product pyrolysis system. While GED data for ketene generated from acetic anhydride has been refined, the species formed from the pyrolysis of Meldrum’s acid were determined to be too difficult to deconvolute without additional experimental data from MS. A computational study of possible ketene derivatives that could be studied with a GED-MS apparatus is also presented.
Lastly, this thesis details a structural study of the gas-phase structures of tris(chloromethyl)amine and a family of substituted disilane systems which have been determined in the gas phase for the first time. A comprehensive GED, Raman spectroscopy and ab initio study have been undertaken for tris(chloromethyl)amine [N(CH2Cl)3] which is shown to have a different structure in the solid and gas phase. Further work in the form of a molecular dynamics investigation has been identified as necessary to describe the low amplitude motion of one of the CH2Cl groups in the gas phase to allow for the GED refinement to be completed. The work on the substituted disilane systems X3SiSiXMe2 (X = F, Cl, Br, I) and X3SiSiMe3 (X = H, F, Cl, Br) demonstrates the effect of increased halogen substitution on the electronic effects of the disilanes, and the effect that the methyl groups have as larger halogens increase the steric bulk of the system.