The work described in this thesis was initiated in an attempt to overcome the limitations imposed upon NMR spectroscopy by magnetic field inhomogeneity in two specific areas: high resolution spectroscopy in isotropic liquids, and chemical shift resolved NMR imaging in isotropic liquids. In both cases magnetic field inhomogeneity may degrade the resolution of spectra to such an extent that no useful information can be obtained from them. In high resolution NMR spectroscopy it is necessary to be able to extract accurately the parameters present within the spectrum such as chemical shifts, coupling constants and peak areas. In chemical shift resolved imaging experiments the requirements are less stringent; and it is only necessary that the resonances of different chemical species be resolved. However, even the less stringent requirements of NMR imaging are often difficult to meet as the sample volumes required are often several orders of magnitude larger than those required in conventional high resolution NMR spectroscopy. The use of zero-quantum coherence has been investigated as a potential solution to the magnetic field inhomogeneity problem in both of these areas. Zero-quantum coherences are independent of magnetic field inhomogeneity and contain the parameters desired in both cases, though they are displayed in a way which differs from conventional NMR spectra. In this thesis, existing zero-quantum coherence experiments have been evaluated for use with inhomogeneous magnetic fields, and, where necessary, adapted for this purpose. Several completely new experiments have been developed for producing broad-band decoupled zero-quantum coherence spectra and also for presenting coupling constants and chemical shifts in a manner which is as close to conventional NMR spectra as possible, hence facilitating ease of use. Zero-quantum coherence has been evaluated as a tool for identifying unknown compounds and also for identifying the components of complex mixtures by "signature" recognition. Both decoupled and non-decoupled zero-quantum coherence experiments are adapted to provide imaging experiments which allow the separation of the images of different chemical species in inhomogeneous magnetic fields. The two-dimensional J-resolved experiment is also adapted for this purpose. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis is divided into two parts: testing and evaluation of some surface coils, and application of the surface coils to in-vivo studies. In particular, the localization properties of surface coils were examined and optimized using the highest performance coil geometry and wire. Application of the surface coil technique to in-vivo studies involved measuring changes in metabolic status of muscle and brain tissue in rats using ³¹P spectroscopy. The properties of surface coils have been studied by evaluating their excitation patterns with ¹H and ³¹P NMR spectroscopy. Surface coils, manufactured in different sizes, geometries, and materials were tested for Q factors, signal-to-noise ratios, and pulse widths required for excitation of the sample. A silver plating on the copper wire used to fabricate the surface coils was found to increase the Q and signal-to-noise of the coil. Examination of the excitation patterns of the surface coils with point samples characterized the B₁ field of the coils as decreasing axially and radially from the coil. Calculations of the magnitude of the B₁ field reveal that its dome-like shape extends to approximately one coil radius above the surface coil. It was found that samples lying outside the domain of this "sensitive volume" did not contribute to a spectrum. These data were all correlated and the "0.9" silver plated coil was deemed to be the most efficient coil with which to pursue further in-vivo studies. In-vivo ³¹P studies of rat tissues were preceded by in-vitro spectral measurements of various metabolites at physiological concentrations. These standards were used to aid in the identification of resonances in the in-vivo spectra. Metabolic changes such as artificially induced ischemia in muscle, deceased brain, and artificially induced brain dementia were compared with "normal" ³¹P spectra of anaesthetized rat tissues. It was found that oxygen deprivation is readily observed with this technique whereas the preparation of brain dementia cannot be diagnosed with ³¹P NMR spectroscopy. / Science, Faculty of / Chemistry, Department of / Graduate

The utility of multivariate analysis methods for the qualitative and quantitative analysis of complex ICP optical emission spectra is shown. A photodiode array is used to collect data which are simplified to a low resolution (approx. 4 A) spectrum for a number of knowns and unknowns. The digitized spectra thus obtained are plotted as points in multivariate space (pattern space). The spectra of different elements appear in well defined regions of pattern space. Qualitative analysis is accomplished by methods of cluster analysis and factor analysis. Quantitative analysis is carried out using multidimensional working curves. The pattern space coordinate system is transformed to give axes corresponding directly to elemental concentrations, allowing direct simultaneous determination of elemental composition. The effect of line intensities, detector dynamic range, and matrix effects are also discussed. / Science, Faculty of / Chemistry, Department of / Graduate

The use of fluorescent molecules as probes of protein conformation is recognized as a technique which provides very specific information and has been applied, in recent years, to the study of the role of tropomyosin (TM) in the regulation of contractile processes. The isolation and sequencing of TM from horse blood platelets (P-TM) has shown it to be different from muscle TM, especially near the NH₂-and COOH-termini. These differences have been suggested to weaken end-to-end interaction of P-TM molecules. TM's are two chain coiled coils and P-TM has cysteine residues at the penultimate COOH-terminus position of adjacent chains. These can be labelled with sulfhydryl-specific fluorescent probes that reflect conformational changes in that region of the molecule via changes in their emission characteristics. The results of experiments on both pyrene (Py) (40) and acrylodan (AD) labelled P-TM show that there is a preferred interaction of the COOH-terminus of P-TM with the NH₂-terminus of cardiac TM over that with the NH₂-terminus of P-TM. This indicates that the altered NH₂-terminus of P-TM, with respect to muscle TM, is responsible for the relative loss of polymerizability of P-TM at low salt concentration. Addition of actin to the Py-P-TM (40) and AD-P-TM species showed changes in emission characteristics indicative of binding to the F-actin filaments, suggesting that the presence of the probes had not affected the function of the P-TM adversely. However, the presence of pyrenes at the COOH-terminus seemed to reduce further the ability of P-TM to self-polymerize. Thermal denaturation of AD-P-TM, AD-C-TM and AD-labelled truncated P-TM followed by fluorescence polarization suggested that, contrary to the theory of Skolnick and Holtzer on the stability of two chain coiled coils, the region towards the COOH-terminus is among the last to lose its helical character. / Science, Faculty of / Chemistry, Department of / Graduate

Electron momentum spectroscopy (EMS) provides experimental atomic and molecular electronic structure information in terms of the binding energy spectrum and the experimental momentum profile (XMP), which is a direct probe of the electron momentum distribution in specific molecular orbitals. The measured XMPs permit a detailed quantitative evaluation of theoretical ab initio wavefunctions in quantum chemistry and also provide a means to investigate traditional concepts in chemical reactivity at the fundamental electronic level. This thesis reports high momentum resolution EMS measurements of the valence orbitals of H₂0, D₂0, NH₃ and H₂CO obtained using an EMS spectrometer of the symmetric, non-coplanar type operated at an impact energy of 1200eV. The measured experimental momentum profiles for the valence orbitals of each molecule have been placed on a common intensity scale, which has allowed a stringent quantitative comparison between experiment and theory. These studies now confirm earlier preliminary investigations that suggested serious discrepancies between experimental and theoretical momentum distributions. Exhaustive consideration of possible rationalizations of these discrepancies indicate that double zeta quality and even near Hartree-Fock quality wavefunctions are insufficient in describing the outermost valence orbitals of H₂0 and NH₃. Preliminary results for H₂CO also indicate that near Hartree-Fock wavefunctions are incapable of describing the outermost 2b₂ orbital. Interactive and collaborative theoretical efforts have therefore led to the development of new Hartree-Fock limit and also highly correlated (CI) wavefunctions for H₂0, NH₃ and H₂CO. It is found that highly extended basis sets including diffuse functions and the adequate inclusion of correlation and relaxation effects are necessary in the accurate prediction of experimental momentum profiles as measured by electron momentum spectroscopy. New EMS measurements are also reported for the outermost valence orbitals of NF₃, NH₂CH₃, NH (CH₃)₂, N (CH₃)₃ and para-dichlorobenzene. These exploratory studies have illustrated useful chemical applications of EMS. In particular, EMS measurements of the outermost orbitals of the methylated amines have revealed chemical trends which are consistent with molecular orbital calculations. These calculations suggest extensive electron density derealization of the so-called nitrogen 'lone pair' in the methylated amines in comparison to the 'lone pair' in NH₃. EMS measurements of the non-degenerate π₃ and π₂ orbitals of para-dichlorobenzene show different experimental momentum profiles consistent with arguments based on inductive and resonance effects. These experimental trends, both in the case of the amines and para-dichlorobenzene, were qualitatively predicted by molecular orbital calculations using double zeta quality wavefunctions. However more accurate prediction of the experimental momentum profiles of these molecules will need more extended basis sets and the inclusion of correlation and relaxation effects as suggested by the studies based on the smaller molecules. An integrated computer package (HEMS) for momentum space calculations has also been developed based on improvements to existing programs. Development studies testing a new prototype multichannel (in the ɸ plane) EMS spectrometer are described. / Science, Faculty of / Chemistry, Department of / Graduate

Some unstable gaseous molecules, cobalt oxide (CoO), niobium nitride (NbN) and aminoborane (NH₂BH₂), were studied by high resolution optical spectroscopy. A portion of the "red" system of CoO, from 7000 Å to 5800 Å, was measured using laser induced fluorescence techniques. Three bands of the system, with origins at 6338 Å, 6411 Å and 6436 Å, were rotationally analyzed. The lower levels of these parallel bands are the Ω = 7/2 and 5/2 spin-orbit components of a ⁴∆i electronic state. Available evidence indicates that this is the ground state of the molecule; its bond length is 1.631 Å. This work completes the determination of the ground state symmetries for the entire series of first row diatomic transition metal oxides. The hyperfine structure in the ground state is very small, supporting a σ²δ³π² electron configuration. The upper state, assigned as σδ³π²σ*, has large positive hyperfine splittings that follow a case (aβ) pattern; it is heavily perturbed, both rotationally and vibrationally. The sub-Doppler spectrum of the ³Φ₋³∆ system of NbN was measured by intermodulated fluorescence techniques, and the hyperfine structure analyzed. Second order spin-orbit interactions have shifted the ³Φ₃₋³∆₂ subband 40 cm⁻¹ to the blue of its central first order position. The perturbations to the spin-orbit components were so extensive that five hyperfine constants, rather than three, were required to fit the data to the case (a) Hamiltonian. The ³∆₋³Φ system of NbN is the first instance where this has been observed. The magnetic hyperfine constants indicate that all components of the ³∆ and ³Φ spin orbit manifolds may be affected, though the ³∆ state interacts most strongly, presumably by the coupling of the ³∆₂ component with the ¹∆ state having the same configuration. The Fermi contact interactions in the ³∆ substates are large and positive, consistent with a σ¹δ¹ configuration. In the ³Φ state the (b + c) hyperfine constants are negative, as expected from a π¹δ¹ configuration. The ³∆ and ³Φ bond lengths are 1.6618 Å and 1.6712 Å, respectively, which are intermediate between those of ZrN and MoN. The Fourier transform infrared spectrum of the V7 BH₂ wagging fundamental of NH₂BH₂ was rotationally analyzed. A set of effective rotational and centrifugal distortion constants was determined, but the band shows extensive perturbations by Coriolis interactions with the nearby V5 and V11 fundamentals. A complete analysis could not be made without an analysis of the V5-V7-V11 Coriolis interactions, which is currently not possible because the very small dipole derivative of the V5 vibration has prevented its analysis. / Science, Faculty of / Chemistry, Department of / Graduate

Chapter II of this thesis describes the operation of a Fourier Transform Ion Cyclotron Resonance Spectrometer. Included is a detailed discussion of software which was developed to run the spectrometer and analyze the data. An automatic data acquisition system for kinetic experiments is also described. Chapter III contains a short discussion of discrete versus continuous methods of data acquisition and problems with the FT-ICR method which utilizes discrete sampling. Two techniques are discussed which have been found to solve problems associated with a digital system, acquisition by "mixing" and zero-filling. Also, mass calibrations done on the FT-ICR spectrometer are presented. The reactions of some negative ions with esters in the gas phase have been studied by FT-ICR and are discussed in Chapter IV. The reactions of ¹⁸0 labelled methoxide with methyl trifluoroacetate, methyl benzoate, dimethyl carbonate, diethyl carbonate and dipropyl carbonate have been studied. It was found that there is incorporation of ¹⁸0 in product ions of the form RCOO⁻ showing that methoxide attacks esters in the gas phase partially at carbonyl carbon. Product distributions are found to be consistent with two competing mechanisms, B[sub AC]2 and S[sub N]2. Thus it was found that CH₃•0⁻ reacts with C₆H₅COOCH₃- 92% by a B[sub AC]2 type mechanism and 8% by an S[sub N]2 type mechanism. The amount of ¹⁸0 incorporation in product ions was seen to decrease with the presence of β hydrogens, due to the presence of an elimination channel. The reaction of ethoxide with the above named esters was studied and the products are also interpreted in terms of three competing mechanisms, B[sub AC]2, S[sub N]2 and elimination. / Science, Faculty of / Chemistry, Department of / Graduate

The microwave absorption spectra of ortho pairs in low ortho concentration samples of solid hydrogen is studied theoretically and experimentally. A theory is developed for several line broadening mechanisms and a comparison made with experiment. Phonon induced lifetime effects are calculated to be less than 2 MHz in the temperature range T=1.2-4.2 K but have not yet been observed experimentally. Inhomogeneous broadening due to isolated ortho molecules and to isotopic mass defect impurities is observed and found to be consistent with theory. Several new lines in the out-of-plane pair configuration are reported which confirm the assignments made previously, whereas two new lines in the next nearest neighbor configuration support a reassignment of these transitions. Also, three excited state transitions which fix the position of the 10 P level are reported and compared with the theoretical predictions of Harris et al. (1977) and Luryi and Van Kranendonk (1979). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Experimental profiles of the He II lines at 3203 Å and 4686 Å have been obtained from a well diagnosed helium plasma. The plasma was produced in a low power z-pinch discharge contained in a vessel of 15 cm diameter and 60 cm length. Uniform plasma columns were located and studied by means of two moveable quartz limiter tubes. The effect of the tubes on the measured electron temperature and density due to cooling and evaporated impurities was measured and the tubes were positioned so as to select a uniform plasma column for study. Electron temperatures were determined from the intensity ratio of the lines He II 4686 and He I 5876 using a theory that considered finite escape probabilities for the Lyman a resonance photons. Electron densities were determined from the width of the He I 5876 line. Corrections were applied for ion broadening due to doubly charged ion perturbers. An electron temperature of 4.0±0.4 eV and an electron density of (6 .1 ±0.6) xl 0 2 3m"^;.wlere determined for the axial plasma occurring soon after the pinch phase. The experimental profile of He II 4686 as measured by a spectrometer-optical multichannel analyzer arrangement was compared to theoretical profiles resulting from a treatment of the electron broadening collisions as single event impacts (Kepple (1972)) and from a treatment of the electron broadening which considers the time development in the collision process (unified classical-path theory) (Greene (1976)). The experimental profile was found to lie midway between the theoretical profiles. Agreement between the experimental and unified classical-path profi1e in the near line wings was good. Agreement between experimental and electron impact results for He II 3203 was not good with a 60% disagreement in line widths. The He II line had a double peak with the peak at shorter wavelengths being 9% higher than the other peak. This is similar to the behavior observed in the Balmer line, Hβ, in the atomic hydrogen spectrum. / Science, Faculty of / Physics and Astronomy, Department of / Unknown

NMR spectra of many systems governed by axially symmetric second rank tensor interactions exhibit P2(cos θ) dependence on the angle 9 between the symmetry axis and the externally applied magnetic field. For the so-called "powder samples" consisting of many randomly oriented domains the resulting spectrum is the superposition of contributions from each such domain. This study deals with a numerical technique enabling one to obtain the lineshapes of such individual contributions responsible for the given powder spectrum. The electric dipolar interaction between two spin 1/2 nuclei produces a characteristic powder lineshape called "Pake doublet", after G.E.Pake, hence the name "de-pake-ing". An iterative algorithm capable of dealing with spectra produced by a variety of systems is developed and checked by applying it to a wide range of simulated NMR spectra. A set of characteristic "signatures" associated with different experimental situations is established and the limits of the applicability of the technique are determined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate