Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 164-178).

No description available.

In this dissertation, I will look into the size distribution of silver nanoparticles produced by laser ablation of microparticles (LAM). I will investigate the role of both pulsed and continuously operating nozzles on the size distribution. In addition, I will examine any deviations from the previously observed log-normal size distribution for silver nanoparticles comparing previous collection techniques involving supersonic jet impaction with a current time of flight mass spectrometer (TOF-MS). These new observations will be made in situ using a Wiley-McLaren TOF-MS with a reflector and multiphoton ionization and will mainly focus on the smaller sized nanoparticles. An introduction to enhancing a second harmonic optically generated signal will also be investigated involving silver nanocomposites while utilizing a polarized crossed-beam femtosecond laser technique. / text

No description available.

This dissertation presents dissociation mechanism and dissociation kinetics studies of gas-phase ions using mass spectrometry (MS). Dissociation of a gas-phase ion is related to its fundamental properties such as composition and structure. However, the detailed processes, internal energy deposition during ion activation as well as the mechanism of dissociation, are not fully known. In the present work, ion structural studies from which mechanisms can be inferred were performed using infrared multiphoton dissociation (IRMPD) spectroscopy, soft-landing, IR spectroscopy, and quantum chemical calculations. Kinetics studies involved instrument modification to add surface-induced dissociation (SID) capability and peak shape analysis. Structural studies were performed to determine dissociation mechanisms. The b₂⁺ ion from AGG is an oxazolone structure as indicated by the IRMPD spectrum and quantum chemical calculations. Protonated 4-ethoxymethylene-2-phenyl-2-oxazolin-5- one is also an oxazolone-type structure, while protonated cyclo-AG is a diketopiperazine structure. Soft-landing experiments were carried out to corroborate IRMPD results. Soft-landed protonated cyclo-AG and protonated 4-ethoxymethylene-2-phenyl-2- oxazolin-5-one underwent neutralization and retained their structures. The soft-landed b₂⁺ ion of AGG showed evidence of ring opening and conversion into a linear structure. The modified matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometers with SID capability were used to study fast dissociation kinetics (sub-microsecond dissociation). Silicon nanoparticle assisted laser desorption/ionization (SPALDI) allows the study of small molecule dissociation kinetics for ions without the matrix interference observed in MALDI. Well characterized systems, such as, N(CH₃)₄⁺, N(CD₃)₄⁺, and substituted benzylpyridinium ions were used to confirm reliability of the peak shape analysis. Obtained dissociation rates, of submicrosecond order, are consistent with the known dissociation theories. Dissociation of fullerenes, C₆₀ and C₇₀, was also investigated with the SID method using a fluorocarbon self-assembled monolayer (FSAM) surface. Fullerene ions produced C(2n)⁺ fragments ion in the kinetic energy range of 150-300 eV. At higher than 400 eV, mass spectra showed additional small fragment ions composed of odd numbers of C units. Energy resolved MS/MS curves support parallel dissociation at high SID energies while peak shape analysis explains sequential dissociation at about 150 eV range. Instrument modification of a MALDI-TOF mass spectrometer with SID capability allowed successful studies of fast unimolecular dissociation kinetics of small ions and fullerenes.

The photodissociation of ozone by ultraviolet light has a great impact on the photochemistry of the atmosphere. The relative quantum yield for the production of the singlet atomic fragment O(¹D) has been determined in the wavelength region 306 to 327 nm for four temperatures between 227 K and 300 K. The technique of resonance enhanced multi photon ionisation (REMPI) was used to probe directly the O(¹D) photolysis product. These relative measurements have been placed onto an absolute scale by the selection of a calibration point whose value has been agreed by the scientific community. The yields obtained are in good agreement with others reported during the time of the research reported in this thesis and clearly show that three mechanisms contribute to the final quantum yield. Below 310 nm, O(¹D) is produced by a spin-allowed channel, above 320 nm the primary channel is a spin- forbidden one and at intermediate wavelengths photolysis of vibrationally excited ozone contributes to the O(¹D) yield. Elements of the quantum yield data presented in this thesis are being included in a new recommendation for the temperature dependent O(¹D) quantum yield. Details of the dissociation kinetics, including further evidence confirming the spin-forbidden channel, is presented in time-of-flight studies of the O(¹D) product. Time-of-flight profiles taken between 317 and 321 nm show evidence that, at room temperature, the O(¹D) quantum yield is anti-correlated with the ozone absorption cross section. Excitation of the O₂(a¹Δ_g) co-fragment has been observed at wavelengths below 296 nm by monitoring the energies of the O(¹D) formed. As the channel for the production of O₂(a¹Δ_g,andnbsp;vandnbsp;=andnbsp;1) opens, it is found that energy is preferentially partitioned into rotation of the O₂ fragment rather than into translation. Initial studies on the O(¹D) fragment have shown that the fragment is orbitally aligned and that the choice of REMPI transition can have a significant effect on the time-of-flight profiles and therefore on the measurements that are made from the profiles. The time-of-flight profiles obtained by probing the O₂(a¹Δ_g) photofragment have shown that the O₂(a¹Δ_g) has an angular momentum polarisation that is J dependent, with the even J being strongly polarised and the odd J depolarised. This results in the shape of the time-of-flight profiles being a function of the REMPI laser polarisation; and the study of this behaviour has been used to confirm the assignments in highly perturbed REMPI spectra.

Thesis (M.S.)--Montana State University--Bozeman, 2004. / Typescript. Chairperson, Graduate Committee: David Dickensheets. Includes bibliographical references (leaves 94-95).

Thesis (M.S.)--University of Missouri--Columbia, 2004. / "May 2004." Typescript. Includes bibliographical references (leaves 30-40). Also issued on the Internet.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 317-343).

Thesis (Ph. D.)--Carleton University, 2000. / Also available in electronic format on the Internet.