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Using both infrared and Raman techniques the vibrational spectra of selected polymorphs of the ammonium halides; NH₄C1, ND₄C1, NH₄Br, ND₄Br, NH₄I and ND₄I, have been recorded in the spectral region 4000 - 50 cm⁻¹. The Raman spectra of NH₄F and ND₄F were also recorded. Although all the foregoing crystals have been the subject of previous spectroscopic investigations some important new features are observed. These include (i) Raman active longitudinal modes and (ii) previously unreported internal and external modes. In addition more meaningful assignments are made for some previously reported spectral lines. Included are assignments involving (i) the non-degenerate NH₄⁺ stretching mode in combination with acoustical modes and (ii) the transverse and longitudinal components of the triply degenerate NH₄⁺ bending mode in combination with the librational mode. A study analagous to that involving the ammonium halides was made of the following alkali-metal borohydrides: LiBH₄, LiBD₄, NaBH₄> NaBD₄, KBH₄, KBD₄, RbBH₄ and CsBH₄. From the vibrational spectrum of potassium borohydride recorded at 10°K it is possible to infer that the ordered phase associated with this salt has a cubic structure compatible with the 2 space group Td² . The vibrational spectrum of the ordered tetragonal phase of sodium borohydride allows the placing of the seven BH₄⁻ (D₂d) internal vibrational modes. In addition a mode of translatory origin is observed and a mode of rotatory origin is inferred from a line assigned as the second overtone of a librational mode. In the case of lithium borohydride seven of the nine BH₄⁻ (C₅) modes are observed. Six modes of translatory origin appear in the infrared and a mode of rotatory origin is inferred from a line assigned as the second overtone of a librational mode. The structure of potassium borohydride at room temperature is discussed and evidence in support of a structure intermediate between the ordered cubic Td² phase and the disordered cubic 0h⁵ phase of sodium borohydride is given. Finally, the F matrix associated with an undistorted XY₄ (Td) (XY₄ = NH₄⁺, BH₄⁻) ion and the G matrix associated with the same ion which has undergone a slight angular distortion to give an XY₄(D₂d) ion is used to calculate the contribution of the kinetic energy to the spectrum of the XY₄ ( D₂d) ion. It is found that the order of appearance in the spectrum of the B₂ and E components associated with the two F₂ vibrations is correctly predicted. / Science, Faculty of / Chemistry, Department of / Graduate

This thesis is concerned with a detailed investigation of the nature, yield, stability, and reactivity of solvated electrons in hexamethylphosphoramide (HMPA). Evidence is presented for their formation by radiolysis and for their comparatively long-lived existence in this highly polar aprotic solvent in which ordinary anions are particularly weakly solvated. By means of microsecond pulse radiolysis methods it was shown that the solvated electron in HMPA has a intense broad structureless absorption band with a band maximum at 2200 ± 100 nm, a band half-width of 3600 cm⁻¹ and maximum molar absorptivity of (3.2 + 0.5) X 10⁴ M⁻¹ cm⁻¹. The spectrum is similar to that found in solutions of sodium metal dissolved in HMPA. Radiolysis studies provided a value of 2.2 ± 0.2 for the free-ion yield of solvated electrons. This was established by both pulse and steady-state methods and is approximately what one would expect on the basis of the liquid's dielectric constant when compared with other solvents. An interesting deduction from the steady-state Ɣ-radiolysis results was that N₂O does not scavenge electrons on a one-to-one basis in this solvent, but rather produced more than one N₂ molecule per electron scavenged. The yields of N₂ from N₂O scavenging of electrons in HMPA/water mixtures are also reported for the full composition range. Electron decays were studied spectro-photometrically and its rate of reaction with N₂O, pyrene, anthracene and other additives are reported in the thesis. When stable solutions of solvated electrons in HMPA (alkali metal solutions) were themselves irradiated, a net decrease in electron concentration occurred, indicating that e⁻HMPA reacts not only with its concomitant positive ion but also with other radiolysis products. Pure HMPA produces hydrogen and methane when irradiated, with yields of 3.3 ± 0.3 and 0.29 ± 0.03 respectively. The H₂ yield was shown to comprise a non-scavengable molecular process (whose yield is 1.4 ± 0.1) and a scavengable part (yield 1.9 ± 0.2) that clearly involved solvated electrons. / Science, Faculty of / Chemistry, Department of / Graduate

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Fouling, slagging, corrosion, and emission of submicron particulate from pulverized coal combustors have been linked to vapor alkali. Size segregated fly ash samples extracted from a 17 kW down-fired pulverized coal combustor showed strong evidence of alkali vaporization. The fraction of sodium in sizes smaller than 0.65 μm (f(8A)) showed a correlation with acid soluble sodium divided by total silicates in the parent coal. Addition of silicates to coal reduced f(8A) for sodium. Potassium existing primarily in the mineral matter, did not show a similar correlation, but f(8A) for potassium did correlate with f(8A) for sodium. Bench scale experiments indicated potassium does not vaporize in the presence of Na or Cl alone, but requires both, and was only released when sodium was captured. Additional of sodium acetate to coal increased f(8A) for potassium. Equilibrium calculations, experiment, and modelling of sodium capture by silicates during pulverized coal combustion identified several important mechanisms governing alkali behavior. The mode of occurrence of alkali in the parent coal dictates its ability to vaporize, its release kinetics, and its sate as it diffuses to the char surface. Other species such as chlorine, sulfur, moisture, and other metals influence alkali stability in the vapor, its reactivity, and its condensation characteristics. Char oxidation can influence alkali vaporization, and capture by affecting included silicate surface area. Sodium reaction with silicates captures from 70 to over 95% of total sodium for typical coals. Silicate additive appears to be a viable technique for reducing the fraction of alkali in the vapor during combustion.

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When trace quantities of an alkali element are added to a flame, its optical and electrical properties change significantly. Addition of alkali seed to both premixed and diffusion flames has been used in the development of two new techniques, one for flame temperature measurement and the other for enhanced mixing. Advantage has been taken of the spectral characteristics of alkali seeds in the development of a non-invasive optical flame temperature measurement technique. The strongest resonance line of alkalis is in fact a doublet, and the two peaks can be subjected to different optical treatment. A cesium-seeded flame was exposed to radiation which was selectively filtered to yield different apparent source temperatures at the wavelengths corresponding to the doublet resonance lines. The ratio of the emission peak heights at the two wavelengths relates directly to flame temperature. This technique allows real-time measurement of flame temperatures up to 2800 K. A second process has been investigated which takes advantage of the enhanced electrical conductivity of alkali-seeded diffusion flames. The study first required a characterization of electrical discharges through planar diffusion flames. Because of the increase in conductivity, alkali-seeded diffusion flames can carry current when a transverse electric potential is applied. The behavior of diffusion flames carrying electrical current has been investigated. The dependence on electrode position and gap is reported and the behavior is contrasted with that described in the literature for premixed flames. A planar diffusion flame was subjected to a steady magnetic field parallel to the flow direction while an orthogonal, oscillating current passed through the flame sheet. A Lorentz body force was induced on the flame sheet which acted to move it alternately toward the fuel and oxidizer streams, improving bulk mixing in the flame. High-speed video images of the oscillating flame were analyzed to obtain its maximum lateral velocity. The results compared well with predictions from a simple theoretical model. / Graduation date: 1992