Thesis (M. Phil.)--University of Hong Kong, 1995. / "9th September 1994." Includes bibliographical references.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed July 6, 2010). PDF text: x, 133 p. : ill. (some col.) ; 3 Mb. UMI publication number: AAT 3366064 . Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Ph. D.)--Tartu University, / Includes bibliographical references.

The microwave spectra of three unstable molecules, bromine isocyanate (BrNCO), iodine isocyanate (INCO), and bromine thiocyanate (BrSCN), have been observed and analyzed in the frequency range 16-54 GHz. The infra-red spectrum of aminodifluoroborane (BF₂NH₂) has been investigated in the region 3700-400 cm⁻¹, and one band, the 2¹₀ vibrational band has been recorded at a resolution of 0.004 cm⁻¹, and the rotational structure analyzed. BrNCO: BrNCO was generated from the flow reaction of Br₂ with silver cyanate. The spectra of two isotopic species were observed: ⁷⁹BrNCO and ⁸¹BrNC0. They contain strong a-type transitions as well as some weaker b-type transitions which could not initially be assigned. In addition, the transitions show both Br and N quadrupole hyperfine structure. A novel method has been developed which uses perturbations in the Br structure to evaluate all the rotational constants, as well as the Br quadrupole tensor, entirely from a-type R branch transitions using a global least-squares fitting programme. This has allowed some b-type transitions to be assigned. The molecule has been shown to be planar and a partial r₀ structure was determined. The principal values of the Br quadrupole tensor have been evaluated and have provided some information about the type of bonding involved in the Br-N bond. INCO: INCO was observed in the flow reaction of I₂ with silver cyanate. Many strong a-type transitions were observed as well as some very weak b-type transitions. These transitions showed I and N quadrupole hyperfine structure; many perturbations in the I structure were observed. The method developed in the analysis of the spectrum of BrNCO using such perturbations to obtain otherwise unobtainable rotational constants was extended to include centrifugal distortion constants. The planarity of INCO has been confirmed and a partial r₀ structure was determined. The principal values of the I quadrupole tensor have been evaluated and have provided some information about the type of bonding involved in the I-N bond. BrSCN: BrSCN was generated in the flow reaction of Br₂ with silver thiocyanate. The spectra contained both a- and b-type transitions, all of which showed Br quadrupole hyperfine structure. The rotational constants and all five quartic centrifugal distortion constants were obtained for two isotopic species: ⁷⁹BrSCN and ⁸¹BrSCN. The rotational constants confirm the thiocyanate configuration, and a partial r₀ structure has been obtained. Also, the principal values of the Br quadrupole tensor were evaluated which show that the Br-S bond is essentially covalent, with small amounts of π and ionic character. BF₂NH₂ : BF₂NH₂ was generated by heating solid BF₃ NH₃. The wavenumbers of 7 of the vibrational fundamentals have been obtained, and from the analysis of the 2¹₀ band, an accurate set of rotational and quartic centrifugal distortion constants of the ground vibrational state have been obtained and the rotational and quartic centrifugal distortion constants of the 2¹ level have been evaluated. Also a Coriolis type perturbation was observed, probably due to the combination level v₇ + v₁₁ , which has provided an estimate of the wavenumber of the v₁₁ fundamental which has not yet been observed. / Science, Faculty of / Chemistry, Department of / Graduate

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The microwave spectra of CH₃I were measured on a C-band Stark cell microwave spectrometer. The lines were analyzed assuming that the quadrupole coupling eQq should be replaced by eQ(aJ(J + 1) + bK² + cK⁴/(J(J + 1)) + d) due to the presence of quadrupole centrifugal distortion. Explicit expressions were derived for a, b, and c in terms of molecular parameters. The values of a, b, and c were calculated for CH₃I and CD₃I and agree reasonably well with the experimental values. An algorithm was devised for the determination of the effect of hyperfine coupling on rotational energy levels in a molecule containing up to four nuclei of arbitrary spin. The uncoupled representation was used, and matrix elements were derived for spin-spin, spin-rotation, quadrupole, and Stark interactions. The case of three equivalent nuclei with spin of 1 was discussed. The microwave spectrum of phosphine-d₂ was measured and analyzed using two structural and three centrifugal distortion constants. Using molecular properties of phosphine, the centrifugal distortion tensor of phosphine-d₂ was calculated and the centrifugal distortion constants were determined. Only one of the three centrifugal distortion constants agreed well with the experimental value, suggesting that more data at higher frequencies is needed. The possibility of an electric hexadecapole interaction in CH₃I was discussed. A relationship between the magnitudes of the electric hexadecapole coupling constant and the d-orbital character of iodine in the C-I bond was derived. A gaussmeter specifically built for the determination of magnetic field in an Electron Paramagnetic Resonance experiment was described. A schematic diagram as well as a discussion of hardware was included.

Gas phase structures and other molecular parameters have been investigated for several molecules and dimers using pulsed beam Fourier Transform Microwave Spectroscopy. An automated control system has been designed and implemented for the microwave spectrometer that has allowed a systematic observation of the microwave spectrum for many molecules. The theoretical models that are available to the gas phase structural chemist, density functional theory and ab-initio methods, are described with detailed comparisons to experimental results. Experimental data was generated for systems involving hydrogen bonded dimers, organic molecules, inorganic molecules and organometallic molecules. Rotational constants and quadrupole coupling constants were determined using the microwave spectra. This data and isotopic investigations have been used to determine key structural parameters and molecular properties.

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