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Browsing by Author "Heinbuch, Scott, author"

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    Desk-top size high repetition rate 46.9 NM capillary discharge laser as photoionization source for photochemistry applications
    (Colorado State University. Libraries, 2006) Heinbuch, Scott, author; Rocca, Jorge J., advisor
    A portable high repetition rate desktop-size capillary discharge laser emitting at a wavelength of 46.9 nm (26.5 eV photon energy) was demonstrated and used as a photoionization source in nanocluster mass spectroscopy. The high photon energy allows the single-photon ionization of nanoclusters and other molecules, which, due to their high ionization potential, would otherwise require undesirable multi-photon ionization. This Ne-like Ar capillary discharge laser occupies a table area of approximately 0.4 x 0.4 m², smaller than that occupied by many widely used ultraviolet gas lasers. The laser's power supplies and gas handling system are designed to fit into small racks that can be placed underneath a standard optical table. The main spark-gap is electrically triggered to allow synchronization of the laser pulses with those of other lasers in photochemistry applications. Experiments were performed to characterize the laser output energy, average power and timing jitter. Tests were conducted to determine the capillary lifetime. Laser pulses with energy ~ 13 μJ were generated at 12 Hz repetition rate by single pass amplification in a 21 cm long Ne-like Ar capillary discharge plasma column. The standard deviation of the jitter was found to be 5 ns. Capillary lifetime tests at 12 Hz repetition rate determined that the laser output energy decays by a factor of two after about 2 10⁴ - 3 10⁴ shots. The laser was installed in a photochemistry laboratory where it is operated for many hours on a daily basis. The laser was successfully used as a single photon photoionization source for the study of hydrogen bonded nanoclusters and other small molecules using time of flight mass spectroscopy. The first mass spectra of water nanoclusters and other small molecules using this source have been obtained.
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    Gas phase cluster studies using a desk-top size soft x-ray laser for single photon ionization
    (Colorado State University. Libraries, 2009) Heinbuch, Scott, author; Rocca, Jorge G., advisor
    This dissertation reports the study of the structure and reactivity of clusters using a new mass spectrometry approach in which the ionization is produced by high energy photons generated by a desk-top size soft x-ray (SXR) laser. The work was motivated by the importance that catalytic processes have in enhancing the rate of gas phase chemical reactions such as the manufacture of hydrocarbons, polymers, drugs, sulfuric acid, fertilizers, pesticides, etc., many forms of pollution control, development of robust mirror coatings for extreme ultraviolet (EUV) lithography, and hydrogen storage for clean energy applications. Extensive mass spectrometry studies have shown that gas phase nanoclusters are effective model systems to study surface reactions in the bulk phase. However, the use of multi-photon ionization or electron impact ionization sources results in cluster fragmentation, limiting the information gained about the neutral cluster parent. Our approach uses the 26.5 eV photons of a compact capillary discharge driven laser to ionize clusters by single photon events, avoiding the cluster fragmentation associated with multi-photon ionization. The high photon energy also allows the detection of neutral clusters and small molecule reaction products with high ionization energies. Experiments were conducted for several types of clusters including van der Waals clusters, metal oxides, and metal oxide reactions. Density Functional Theory (DFT) calculations were employed to elucidate cluster geometries, properties, and reaction mechanisms. For hydrogen/van der Waals clusters, the unimolecular dissociation rate constants for reactions involving loss of one neutral molecule were calculated and neutral cluster temperature were estimated. The results of metal oxide clusters experiments and calculations suggest that SO2 can be reduced and oxidized by oxygen deficient and oxygen rich vanadium oxide clusters, respectively. Three SO3 formation mechanisms are proposed, and several condensed phase catalytic cycles are suggested based on SO3 formation mechanisms. Other experiments showed that C=C bonds of alkenes can be broken on neutral vanadium oxide oxygen rich clusters with the general structure VO3(V2O 5)n=0,1,2.... DFT calculations provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes are broken. New results also help to elucidate the selective catalytic reduction of NO using NH3 on a vanadium oxide catalyst. A separate set of experiments to identify capping layer materials for extreme EUV optical coatings that are resistive to carbon contamination. Results show that oxidized Hf and Zr are much less reactive than Ti or Si oxide, and might lead to capping layers that might extend lifetimes of EUV mirror coating upon EUV irradiation. Zr oxide was found to be less reactive than Hf oxide. The set of results demonstrate the potential of compact soft-ray lasers as new tools for chemistry and photo-physics studies with intense soft x-ray light in small laboratory environments.