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Investigations by 19 F broadline magnetic resonance Cyr, Theodore J. R.

Abstract

The work reported here is: 1) a detailed study of the ¹⁹F nuclear magnetic resonance (n.m.r.) spectra of KPO₂F₂. The temperature dependence of the second moment and line width is interpreted in terms of reorientation of the PO₂F₂⁻ anion in the crystal lattice. A detailed analysis of the line shape at low temperatures is used to yield the interatomic spacings of the PF₂ fragment in the PO₂F₂⁻ anion. 2) an investigation of the n.m.r. adiabatic rapid passage technique as a quick and simple method for determining nuclear Zeeman spin-lattice relaxation times, T₁. The limitations of the experiment are examined and correction formulae are presented. The temperature dependence of T₁ is observed for the globular molecules, exo- and endo-pentadienyl maleic anhydride, for the fatty acid soap, lithium stearate, and for the inorganic salt, KPO₂F₂. The data are interpreted to yield some of the kinetics of molecular motion in these solids. 3) a ¹⁹F nuclear magnetic resonance investigation of polycrystalline K₂NbF₇ and K₂TaF₇, yielding some of the kinetics of molecular motion. The crystal structures, as seen by n.m.r., are found to be essentially identical. 4) an investigation of the ¹⁹F n.m.r. spectra of paramagnetic RhF₅. and IrF₅. This study has been reasonably successful in elucidating the molecular configuration of these substances, a problem uniquely suitable to the n.m.r. technique and insoluble to most other methods of structural analysis. The very large resonance shifts are interpreted in terms of unpaired electron density at the fluorine atoms. 5) a brief examination of the electron spin resonance spectra of X-irradiated polycrystalline KPO₂F₂ and Na₂PO₃F. Two anion radicals, PO₃⁼ and PO₂F⁻ , are identified and, within certain approximations, the nearly isotropic hyperfine coupling constants are evaluated and interpreted in terms of unpaired electron spin densities at the magnetic nuclei. Presentation of Data The organization of this dissertation differs from the form usually found. The justification offered in its behalf is that the topics covered can more easily be listed in a horizontal rather than a vertical array. Therefore, the presentation, theoretical comparison and discussion of the data have been grouped together for each topic. The order in which topics are considered depends on their priority in common discussion and their interdependences. The first to be considered is the n.m.r. line shape of the fluorine resonance in KPO₂F₂. Then, using experimental results as a guide, a determination of the interatomic distances is attempted. The temperature dependences of the n.m.r. line shape is presented and a model describing the type of molecular motion is sought. An explanation of the adiabatic rapid passage technique is then considered because it is used to obtain the spin-lattice relaxation time data. The spin-lattice relaxation time data of ¹⁹F in CaF₂ and KPO₂F₂ and of the ¹H in lithium stearate and endo- and exo-pentadienyl maleic anhydride are then considered. The limits of applicability of the adiabatic rapid passage technique are considered. The n.m.r. line shape of the fluorine resonance in K₂NbF₇ and K₂TaF₇ and its variation with temperature are interpreted in terms of molecular motion. A modified line width-correlation frequency equation first derived by Bloembergen, Purcell and Pound is used to derive an activation energy describing the hindered reorientation of the NbF₇⁼ and TaF₇⁼ anions in the low temperature solids. The n.m.r. line shape of the fluorine resonance in IrF₅- and RhF₅ is used to elucidate the molecular structure, a problem uniquely suitable to n.m.r. The large resonance shifts of the fluorine resonances may be used to obtain the unpaired electron density at the fluorine nuclei. The e.s.r. line shape observed for X-irradiated polycrystalline KPO₂F₂ and Na₂PO₃F is interpreted in terms of the •PO₂F⁻ and the •PO₃⁼ radicals, respectively. The hyperfine coupling constants are obtained and the electron density at the phosphorous and fluorine atoms are estimated.

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