Volcanogenic lightning has a long documented history in the scientific field, though its origins are still poorly understood. The interactions leading to electrification of ash plumes is essentially a function of the microphysics controlling and affecting ash particle collisions. This thesis presents measurements made on charged particle interactions in a fluidized bed, with large-scale applications to the phenomenon of volcanogenic lightning and charged particle dynamics in volcanic plumes. Using a fluidized bed of ash samples taken from Ecuador's Volcán Tungurahua, particles are introduced to a collisional environment, where they acquire an associated polarity. A charged copper plate is used to collect particles of a given polarity, and particle size distributions are obtained for different weight fractions of the ash. It is observed that relatively smaller particles acquire a net negative charge, while larger particles in the sample charge positively. This is a well-documented occurrence with perfectly spherical, chemically identical samples, but this work represents one of the first applications of the principle to volcanic ash. Image analysis is preformed to determine the size distribution associated with specific polarities, and the associated minimum charge on each particle is calculated based on the plate collection height and particle size. We also present results that demonstrate the relationship between particle collisions and the amount of charge exchanged. Using techniques developed to examine the collision rate within a flow, combined with the charging rates determined from this experiment, we determine a maximum charge exchange rate of 1.28±0.23 electrons transferred per collision.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 164-177).

Photosystem II (PSII) is the membrane-bound oxidoreductase peptide complex responsible for the oxidation of water to molecular oxygen and reduction of plastoquinone to plastoquinol. Primary electron transfer is initiated upon absorption of a photon by the primary donor chl resulting in electron transfer and production of a P680+QA charge separated state. P680+ is reduced by YZ (Y161 of the D1 polypeptide subunit), one of two redox-active tyrosine residues found in PSII. This produces a neutral tyrosyl radical (YZ ) which is subsequently reduced by electrons derived from water at the oxygen-evolving complex (OEC). The OEC is composed of four manganese, one calcium ion, and one chloride ion. Four photons are required to convert water to O2, each photon advancing the OEC through successive oxidation states or S states. The exact chemical mechanism of water oxidation in PSII is not known. However, proton-coupled electron transfer (PCET) is thought to be one of the fundamental steps in driving the extraction of electrons and protons from water. Here, the mechanism of water oxidation is investigated with focus on PCET events using vibrational spectroscopy. Vibrational spectroscopy is sensitive to changes in protein structure, charge, and hydrogen bonding, and is ideal for the study of fast events coupled with light-induced electron transfer. The results presented here demonstrate the utility of time-resolved infrared spectroscopy in the detection of intermediates of photosynthetic water oxidation. We suggest that proton transfer may precede manganese oxidation during water oxidation based on time-resolved infrared and difference FT-IR spectroscopic results. The mechanism of PCET associated with YZ reduction is investigated. Using reaction-induced difference FT-IR spectroscopy, the identity of the chloride binding site is speculated through the use of bromide exchange at the OEC. Also, proton transfer reactions at the OEC are investigated using azide as a vibrational probe. The advances in the understanding of photosynthetic water oxidation gained in this work will aid in the elucidation of the chemical mechanism of this important reaction. Understanding the details of photosynthetic water oxidation will assist in the development of technology aimed at harnessing the energy of the sun for the benefit of humankind.

M.Sc. / Donor-acceptor (D-A) systems consist of a donor covalently or non-covalently linked to an acceptor. The simplest D–A system consists of a donor linked to an acceptor and is called a dyad system. Photoactive dyad systems are molecular devices designed to perform through the separation of charge separation states and the conversion of solar energy to chemical energy in analogy to photosynthesis.1 These dyad systems consist of a donor which is usually a chromophore and an acceptor. The design of these systems is guided to mimic photo-induced electron transfer (PET) and charge separation (CS), which are fundamental processes of photosynthesis. In nature, photosynthetic units are often built from dyads consisting of pigments like chlorophyll (donors), non–covalently linked to quinones, (acceptors). The donor harvests light energy and transfers the energy to the nearby pigment molecules until it eventually reaches a special region of the chlorophyll macrocycle called the reaction centre where this light energy is then converted to electrochemical energy. Photoactive dyad systems act as artificial photosynthetic models as they reproduce photo–induced electron transfer and charge separation of natural photosynthesis. In this project, dyad systems were made by covalently linking zinc pheophorbide, a modified chlorophyll derivative to double–walled carbon nanotubes (DWCNTs). Zinc pheophorbide acts as the donor and DWCNTs as the acceptors. Chlorophyll was modified by cutting the phytol chain and inserting zinc as the central metal to yield zinc pheophorbide. This derivative is stable against irradiation, has a good range of acceptor wavelength and is also a good light harvester. DWCNTs are one dimensional nanowires with two concentric tubes. They readily accept electrons because they have an extended π electron system. These electrons are then transported efficiently under ballistic conditions. DWCNTs were synthesised by catalytic chemical vapour deposition (CCVD) of methane over Mg0.99Co0.075Mo0.025O catalyst. In dyad system 1, amidated zinc pheophorbide molecules were covalently attached to oxidised DWCNTs in the presence of N–ethyl–N’–(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) \ and N–hydroxysuccinnimide (NHS) as a catalysts. Dyad system 2 was synthesized by attaching zinc pheophorbide molecules to amidated DWCNTs using the same catalysts.

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In dieser Arbeit werden hochgeladene, mit einer Electron Beam Ion Trap produzierte Ionen für die Erforschung des Elektroneneinfangs von Oberflächen und Gasen eingesetzt. Die Untersuchungen mit Gastargets konzentrieren sich auf die Energieabhängigkeit der Verteilung der K-Schalen-Röntgenstrahlen, die nach Elektroneneinfang in Rydberg-Zustände von Ar-17+ und Ar-18+ Ionen am Ende einer Kaskade von Elektronenübergängen entstehen. Die Ionen werden von der Ionenquelle mit einer Energie von 2 keV/u extrahiert, ladungsselektiert und anschließend bis auf 5 eV/u abgebremst, um dann mit einem Argon Gastarget zu interagieren. Für abnehmende Stoßenergien wird eine Verschiebung des Elektroneneinfangs in Zustände mit niedrigen Drehumpulsquantenzahlen beobachtet. Zum Vergleich wird auch die K-Schalen-Röntgenstrahlung auf Grund des Elektroneneinfangs bei Ar-17+ und Ar-18+ von dem Restgas in der Falle gemessen. Dabei wird eine Diskrepanz zu den Resultaten der Extraktionsversuche festgestellt. Mögliche Erklärungen werden diskutiert. In den Untersuchungen zum Elektroneneinfang von Oberflächen werden hochgeladene Ionen von der Ionenquelle mit Energien von 2 bis 3 keV/u extrahiert, ladungsselektiert und auf Targets gelenkt. Diese bestehen aus Siliziumnitridmembranen mit einer Vielzahl nanometergroßer Löcher, welche mittels eines fokussierten Ionenstrahls in Kombination mit ionenstrahlinduzierter Abscheidung dünner Filme erstellt werden. Es werden hierbei Lochdurchmesser von 50 bis 300 nm mit Formfaktoren von 1:5 bis 3:2 erreicht. Bei den hochgeladenen Ionen handelt es sich um Ar-16+ und Xe-44+. Nach dem Transport durch die Kapillare passieren die Ionen einen elektrostatischen Ladungstrenner und werden detektiert. Der Anteil des Elektroneneinfangs von den Wänden der Löcher ist weitaus geringer als Modellberechnungen vorhersagen. Die Resultate werden an Hand eines Kapillareffekts zur Ionenleitung diskutiert. / In this study highly charged ions produced in Electron Beam Ion Traps are used to investigate electron capture from surfaces and gases. The experiments with gas targets focus on spectroscopic measurements of the K-shell x-rays emitted at the end of radiative cascades following electron capture into Rydberg states of Ar-17+ and Ar-18+ ions as a function of collision energy. The ions are extracted from an Electron Beam Ion Trap at an energy of 2 keV/u, charge-selected and then decelerated down to 5 eV/u for interaction with an argon gas target. For decreasing collision energies a shift to electron capture into low orbital angular momentum capture states is observed. Comparative measurements of the K-shell x-ray emission following electron capture by Ar-17+ and Ar-18+ ions from background gas in the trap are made and a discrepancy in the results compared with those from the extraction experiments is found. Possible explanations are discussed. For the investigation of electron capture from surfaces, highly charged ions are extracted from an Electron Beam Ion Trap at energies of 2 to 3 keV/u, charge-selected and directed onto targets comprising arrays of nanoscale apertures in silicon nitride membranes. The highly charged ions implemented are Ar-16+ and Xe-44+ and the aperture targets are formed by focused ion beam drilling in combination with ion beam assisted thin film deposition, achieving hole diameters of 50 to 300 nm and aspect ratios of 1:5 to 3:2. After transport through the nanoscale apertures the ions pass through an electrostatic charge state analyzer and are detected. The percentage of electron capture from the aperture walls is found to be much lower than model predictions and the results are discussed in terms of a capillary guiding mechanism.

The field of organic electronics, in which -conjugated, organic molecules and polymers are used as the active components (e.g., semiconductor, light emitter/harvester, etc.), has lead to a number a number of key technological developments that have been founded within fundamental research disciplines. In the Dissertation that follows, the research involves the use of quantum-chemical techniques to elucidate fundamental aspects of both intermolecular and intramolecular electron-transfer processes in organic, -conjugated molecules. The Dissertation begins with an introduction and brief review of organic molecular systems used as electron-transport semiconducting materials in device applications and/or in the fundamental studies of intramolecular mixed-valence processes. This introductory material is then followed by a brief review of the electronic-structure methods (e.g., Hartree-Fock theory and Density Functional Theory) and electron-transfer theory (i.e., semiclassical Marcus theory) employed throughout the investigations. The next three Chapters deal with investigations related to the characterization of non-rigid, -conjugated molecular systems that have amorphous solid-state properties used as the electron-transport layer in organic electronic and optoelectronic devices. Chapters 3 and 4 involve studies of silole- (silacyclopentadiene)-based materials that possess attractive electronic and optical properties in the solid state. Chapter 5 offers a preliminary study of dioxaborine-based molecular structures as electron-transport systems. In Chapters 6 8, the focus of the work shifts to investigations of organic mixed-valence systems. Chapter 6 centers on the examination of tetraanisylarylenediamine systems where the inter-redox site distances are approximately equal throughout the series. Chapter 7 examines the bridge-length dependence of the geometric structure, charge-(de)localization, and electronic coupling for a series of vinylene- and phenylene-vinylene-bridged bis-dianisylamines. In Chapter 8, the role of symmetric vibrations in the delocalization of the excess charge is studied in a dioxaborine radical-anion and a series of radical-cation bridged-bisdimethylamines. Finally, Chapter 9 provides a synopsis of the work and goals for future consideration.

In recent years, improved control of the motional and internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Many-body effects have been explored with hundreds of thousands of quantum-degenerate neutral atoms and coherent light-matter interfaces have been built. Systems of single or a few trapped ions have been used to demonstrate universal quantum computing algorithms and to detect variations of fundamental constants in precision atomic clocks. Now in our experiment we investigate how the two systems can be advantageously combined. We immerse a single trapped Yb+ ion in a Bose-Einstein condensate of Rb atoms. Our hybrid setup consists of a linear RF-Paul trap which is overlapped with a magnetic trap and an optical dipole trap for the neutral atoms. A first synergetic effect is the sympathetic cooling of the trapped ions to very low temperatures through collisions with the ultracold neutral gas and thus without applying laser light to the ions. We observe the dynamics of this effect by measuring the mean ion energy after having an initially hot ion immersed into the condensate for various interaction times, while at the same time monitoring the effects of the collisions on the condensate. The observed ion cooling effect calls for further research into the possibility of using such hybrid systems for the continuous cooling of quantum computers. To this end a good understanding of the fundamental interaction processes between the ion and the neutrals is essential. We investigate the energy dependent elastic scattering properties by measuring neutral atom losses and temperature increase from an ultracold thermal cloud of Rb. By comparison with a Monte-Carlo simulation we gain a deeper understanding of how the different parameters affect the collisional effects. Additionally, we observe charge exchange reactions at the single particle level and measure the energy-independent reaction rate constants. The reaction products are identified by in-trap mass spectrometry, revealing the branching ratio between radiative and non-radiative charge exchange processes.

No description available.