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published_or_final_version / Physics / Master / Master of Philosophy

The vacuum ultraviolet molecular hydrogen laser is evaluated as a selective ion source for analytical mass spectrometry of easily-ionized compounds. The types of compounds ionized below the photon energy of 7.8 eV include polynuclear aromatic hydrocarbons, and many amines and nitrogen-containing heterocycles. The latter two categories encompass a large number of pharmaceuticals and drugs of abuse. H₂ laser photoionization produces parent molecular ions only, for all compounds studied thus far. Selectivity of the threshold photoionization process is very high, as compounds within as little as 0.2 eV above the threshold are completely rejected. The ability of the technique to discriminate against interfering matrix components is demonstrated for both simple synthetic and complex "real world" mixtures. Easily interpreted spectra are obtained from simple extracts of spiked coffee, beer, soy sauce, urine and blood serum. The most important interference is shown to be electron impact ionization arising from acceleration of stray electrons in the ion source. Most of this ionization is caused by low-energy secondaries generated when stray primaries are collected by the ion source electrodes. The primaries are produced mainly by interaction of scattered laser radiation with metal surfaces. This interference can be controlled through proper instrumental design.

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The thesis concerns experimental studies of discharge excited lasers operating in the vacuum ultraviolet (VUV) region of the spectrum. The known molecular fluorine laser operating at 157nm, on a bound- to-bound transition of the F₂ molecule was selected for initial study. As a result of the work reported here the energy per pulse was increased by a factor of five (10mJ to 50mJ) from that of earlier F₂ lasers. Similary the working lifetime of the gas mixture was increased from a few shots to several thousand by the application of cryogenic gas purification techniques. These improvements have resulted in the development of a practical commercial F₂ laser. The performance characteristics of the fluorine laser and their relationship to the physical mechanisms are discussed. With the objective of achieving laser action in the 110 to 130nm region of the VUV a novel scheme is investigated. The scheme involves the production of a population inversion between the v'=1 level of the b¹π_u state of molecular nitrogen and high lying levels of the X¹Σ_g ground state. The excitation of the upper laser level involves production of N₂ molecules in the a¹π_g state by means of a pulsed discharge. Transfer of population from this intermediate 'a' state to the upper level is accomplished by absorption of radiation at 308nm from a discharge excited xenon chloride laser. The practicality of this scheme has been investigated to the extent that populations of the order of 10¹³ molecules per cm³ have been produced in the 'a' state and laser induced fluorescence on the 'b' to 'X' band has been observed. Under the conditions of "the present experiments the potential VUV gain is too small (10^-4cm<sup>-1>/sup>) to reach laser threshold. The problems of increasing the gain to reach threshold for a practical device are discussed.

Thesis (Ph. D.)--University of Adelaide, Dept. of Physics, 1983. / Includes bibliographical references (leaves [250]-268).

Thesis (M.S. in Physics)--Naval Postgraduate School, December 1990. / Thesis Advisor(s): Cleary, David D. ; Davis, D. Scott. "December 1990." Description based on title screen as viewed on April 2, 2010. DTIC Identifier(s): Ionosphere, Ultraviolet Spectroscopy, Interferometer. Author(s) subject terms: Ionosphere, Ultraviolet Spectroscopy, Interferometer. Includes bibliographical references (p. 64-67). Also available in print.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: C. Grant Willson. Vita. Includes bibliographical references.

Call number: LD2668 .T4 1961 B89

Four different trivalent and tetravalent metal phthalocyanine systems (chlorogallium, chloroindium, vanadyl, and titanyl phthalocyanines) were used singly to prepare thin films (0.05-2.0 micron thickness) on gold, optically transparent substrates. The photoelectronic properties of these electrodes could be modified either by altering the growth conditions (i.e. rate of sublimation, cleanliness of substrate) or by dosing the thin films with either hydrogen or oxygen at elevated temperatures (150°C). The properties of these thin films were monitored by electron microscopy, UV-visible spectrophotometry, X-ray and Ultra-violet surface spectroscopies, and a variety of electrochemical and photoelectrochemical techniques. All four systems behaved in a manner similar to a p-type semiconductor when prepared at rapid rates (10-20 A/min) on gold substrates. In the dark, for contacting redox couples with Eᵒ’ values negative of +0.6V, the phthalocyanine electrodes showed negligible dark currents. Upon illumination, the photoelectrodes only produced positive photopotentials. Chlorogallium phthalocyanine thin films could be made to produce both positive and negative photopotentials when grown at slow rates (1-5 A/min) on clean, gold substrates. These chlorogallium phthalocyanine electrodes regained the properties of a p-type semiconductor after being dosed with oxygen for 48 hours at 150°C. X-ray Photoelectron Spectroscopy confirmed the presence of a high concentration of oxygen at the surface of all of the p-type phthalocyanine electrodes. The oxygen may accept electron density from the phthalocyanine macrocycle to cause the Fermi level to move down in energy toward its valence band edge. Dosing the film with hydrogen caused the electrode to exhibit its original intrinsic characteristics. This variability in electrical properties as a function of gas dopant may lead to the development of a sensitive gas sensing device. Ultra-violet Photoelectron Spectroscopy, as well as molecular orbital calculations, were applied to the chlorogallium phthalocyanine system to determine the molecular orbital contributions to its valence and conduction bands. Photoelectrochemical cells made from electrodes of chlorogallium and vanadyl phthalocyanines exhibited power conversion efficiencies in excess of 0.1%. The vanadyl and titanyl phthalocyanine electrodes were also effective catalysts for the photoreduction of H⁺ to H₂.