Photographic and Photoelectric measurements were made on the shock excited spectra of Argon and Helium. The plasma temperature and electron density in the region behind the shock wave were calculated from the spectroscopic measurements. These quantities were compared with the values obtained from the Rankine Hugoniot shock theory including the effect of ionization. Considerable disagreement was found between experimental results and theoretical predictions. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The pure rotational spectrum of difluorochloromethane, Freon 22, has been obtained in the K-band microwave region with a Stark modulation spectroscope. Over two hundred spectrum lines, of which the majority are grouped into doublets or quadruplets, have been found. Fifteen doublets and one quadruplet correspond in frequency with previous determinations but the majority of the lines and structures have not previously been recorded. In addition, a definite sestet of lines and two definite triplets have been noted. The grouping into multiplets has been made possible by similarities in the line shape, in the Stark modulation response, and in the effects of chilling the Stark cell with dry ice. The latter effect has been the most important factor in identifying several transitions involving low values of J, the total angular momentum quantum number. The sestet and two quadruplets have been found to be the result of the interaction of the Cl³⁵ quadrupole moment with the electrostatic potential at the site of the nucleus. The sestet represents six of the possible eight lines for a transition from a J=1 rotational level to a J=2 level. The quadruplets represent two transitions involving only J=3 rotational levels. From these three structures have been obtained the complete solution for the spectrum of the molecule containing CI³⁵ and the values of the components of the quadrupole coupling constant for the CI³⁵ nucleus along the principal axes of the angular momentum ellipsoid. In all, eight multiplets have been correctly identified for the molecule containing Cl³⁵ and the two theories of the rotational levels and of the hyperfine structure for an asymmetric top molecule have been verified. From the rotational constants for the molecule containing CI³⁵ the values for the molecule containing CI³⁷ can be closely estimated and the rotational spectrum for the latter case has accordingly been predicted with considerable accuracy. By means of the predicted values, five multiplets and one single line have been identified for the molecule containing CI³⁷ and the theories for the rotational levels and for the hyperfine splittings can be rechecked. From the spectra for the two molecules, five independent rotational constants have been obtained with a precision that compares favourably with the precision of other experimenters in the field of microwave spectroscopy. With these five constants and an approximation to the carbon-hydrogen bond length, the structure of the molecule has been calculated with an accuracy much better than that obtained from electron diffraction measurements. The quadrupole coupling constant for CI³⁵ in Freon 22 has been found to be -71.6 ± 0.5 Mc/s, a value which is about 1 Mc/s larger than the value for the molecule in the solid state. The difference between the components of the quadrupole coupling tensor along two axes perpendicular to the carbon-chlorine bond has been found to be rather small in comparison with the value suggested by bond theory. Some comments are offered on the nature of the chemical bond in the light of these electric quadrupole moments for CI³⁵ and the bond lengths for the carbon-chlorine and carbon-fluorine bonds which have been calculated to be 1.7576 ± .0093 Å and 1.3405 ± .0058 Å respectively for Freon 22. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Standard techniques of radio-frequency nuclear resonance spectroscopy have been applied to further studies of the interaction between atomic nuclei in crystals and the crystalline electric' field gradients at the nuclear sites. Observations have been made on the nuclear magnetic resonance spectra of Al²⁷, Li⁶, Li⁷ and Si²⁹ in single crystals of LiAl(Si0₃)₂ (spodumene) in strong magnetic fields. Results from the Al²⁷ spectrum provided improved values of the field gradient constants of spodumene and a check on the adequacy of second and third order perturbation theory in describing the electrostatic perturbation of the magnetic energy levels; these results also provided an experimental check on a proposed new method of nuclear spin determination. The Li⁶ and Li⁷ measurements provided a more accurate value of the quadrupole moment ratio for this pair of isotopes. Observations on the Si²⁹ spectrum support; existing evidence that the spin of Si²⁹ is 1/2. A super-regenerative spectrometer has been built for the detection of nuclear magnetic resonances and nuclear electric quadrupole resonances. Preliminary tests indicate that it will detect resonances in solids at low frequencies which could not be detected with the continuous-wave type of spectrometer. A pure quadrupole resonance in Na₂B₄O₇.4H₂O (kernite) has been detected at 1.27 Mc./sec. using this super-regenerative spectrometer. This represents a pure quadrupole resonance of the lowest frequency reported to date. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Lubzinski.spectrograph has been accurately focussed and its performance as a high dispersion vacuum ultraviolet instrument has been studied. Light sources have been designed for the excitation of the hydrogen Lyman series. The α line of this series has been obtained using exposure times ranging from twenty minutes to seven hours. A spectrogram of the hydrogen-deuterium isotope structure obtained in the fifth grating order at a dispersion of 1 A°/mm. has been obtained permitting positive identification of the hydrogen Lyman α line. Light sources for the excitation of the first-spark spectra of copper have, been constructed and experimentally studied. This spectrum contains a large number of standard wavelengths, in the vacuum ultraviolet; however, because of low grating intensity we were unable to observe these lines. An existent discrepancy between calculated and measured, values for the ionization potential of Helium-like atoms has been resolved by a generalized Lamb electromagnetic shift. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The beta and gamma spectra of Fe⁵⁹ have been examined in a thin lens beta ray spectrometer. Gamma rays with energies of 1.10 Mev and 1.29 Mev were detected using the photoelectric technique with a Uranium radiator. Using a thin foil as a source, beta groups with maximum energies of 1.77 Mev and 0.45 Mev were found. There was no evidence of a 0.26 Mev group as reported by other workers. Tentative decay schemes are presented. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No abstract included. / Science, Faculty of / Mathematics, Department of / Graduate

The 584 Å photoelectron spectra from eight polyatomic molecules (CH₃I, CH₃Cl, CH₃Br, CH₃CHO, CH₃COCH₃, SF₆, CH₃CN and C₂H₅CN) are described and shown to give all the ionization potentials less than 21.21 eV in each case. The results are interpreted in terms of the electronic structures of these molecules as given by molecular orbital theory. They are compared with results from other sources, and agreements and differences explained. A brief account of other existing methods used for the determination of ionization potentials with their advantages and disadvantages is given. The major components of the instruments are briefly discussed, and use of a Single-Grid Photoelectron Spectrometer in the detection of fine structure in the photoelectron spectra is pointed out. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

The aquatic filamentous bacteria (Cyanobacterium) Lyngbya majuscula is a nitrogen-fixer found in coastal waters often attached or adjacent to sea grass, algae and coral. It is characterized by phycobiliproteins, unique pigments found only in cyanobacteria. To sustain photosynthesis and nitrogen fixation, L. majuscula requires iron proteins and is therefore sensitive to the availability of this metal. The hypothesis tested in this study concerns the potential use of hyperspectral imaging in detecting L. majuscula in coastal regions as biological indicators for the presence of iron debris or metal objects in the littoral environment. This concept would have potential benefits and applications in mine detection and countermeasure techniques. Using a USB2000 field spectroradiometer, a spectral library was developed for the benthic substrates of Midway Atoll, Northwest Hawaiian Islands, spectrally characterizing L. majuscula and the surrounding coral reef substrates. The data was analyzed to determine unique spectral characteristics of the benthic cyanobacteria in a mixed coral environment and evaluated against the resampled spectral resolution of a number of hyperspectral sensors: Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), Hyperspectral Mapper (HyMap) and Compact Airborne Spectrographic Imager (CASI). The results of the in situ spectroscopy suggest a strong potential for all three sensors to detect these cyanobacteria in a mixed coral reef environment at four distinct wavelengths attributable to phycobiliprotein pigment absorptions unique to cyanobacteria. Of these four discriminative absorption ranges, the phycoerythrin absorption of 565-576 nm shows the greatest potential for segregating cyanobacteria from a mixed algal/ coral / sand environment so long as the coral Montipora spp. is not present within the scene, since it has an overlapping absorption in those wavelengths. In the presence of Montipora corals, these cyanobacteria are more difficult to detect. However, in a mixed environment composed of L. majuscula and Montipora corals, the cyanobacteria can be distinguished by a different phycocyanin absorption, at 615-632 nm.