No description available.

Simple models for bright, helium producing phases in the lives of massive galaxies are used to investigate the distance out to which they could be seen as individual objects. Roughly speaking, objects radiating at effective temperatures of ..;40,000 o could be detected out to redshifts as large as 8 -+12. Such redshifts correspond to densities at which we might reasonably have expected galaxy condensation to occur, except possibly for the lowest part of the probable range of go-values. Such Objects ought to be bluer than ordinary "nearby" galaxies, and for open cosmological models would be expected to be much more numerous than ordinary galaxies; for closed models the numbers of bright and ordinary galaxies should be comparable. The feasibility of detecting such objects by ground -based measures of their integrated skybrightness in the L and M windows is discussed, and it appears that such a technique would be feasible and superior to direct photographic detection only for relatively low effective temperatures in the 20,000 to 1+0,000 range. The possibility of explaining the lack of general Ljy -c4 absorption in distant WO as due to a high degree of ionization brought about by W radiation from these bright galaxies is investigated. The conclusion is that this mechanism will not usually be adequate -- and when it is adequate, the objects causing the ionization should be detectable -- unless the current mean density of uncondensed gas is very low, of the order of 10 -7 particles /cm3 or less.

The recombination rate coefficient for molecular helium ions has been measured in a pulsed afterglow at 1.86 Torr as a function of electron temperature and electron density without making a priori assumptions about the functional dependence. The concentrations of the molecular ions and electrons were measured and the source terms for the molecular ions were included in the rate equation.

Organic aerosols are ubiquitous to the lower atmosphere and there is growing concern about their impact on climate and human health. These aerosols typically have multicomponent compositions that change over time in part due to oxidation by reactive trace gases, such as ozone. A current challenge to the atmospheric research community is to develop better methods of analysis of these particles. Photoelectron resonance capture ionization aerosol mass spectrometry (PERCI-AMS) is an online mass spectrometric method that has been applied to the analysis of organic aerosols. One of its key advantages is that it employs low energy (~ 0 eV) photoelectrons in the ion forming process, which has been shown to minimize fragmentation in the organic analytes, thus simplifying mass spectral interpretation. This dissertation focuses on the application of PERCI-AMS to the analysis of organic particles. Initial emphasis is placed on the heterogeneous reaction of gas phase ozone with liquid oleic acid particles. Products identified included carboxylic acids, aldehydes, and peroxides including alpha-acyloxyalkyl hydroperoxides polymers. The evidence of peroxidic products suggested the stabilization of carbonyl oxide intermediates (i.e. Criegee intermediates) that are formed during ozonolysis. Subsequent PERCI-AMS experiments investigated the reactivity of the stabilized Criegee intermediates. This included investigating the reaction of Criegee intermediates with unsaturated fatty acids and methyl esters. A novel ketone-forming reaction is described in these systems, suggesting the Criegee intermediates can react at a carbon-carbon double bond. Further PERCI-AMS experiments investigated the oxidative processing of particulate amines including octadecylamine and hexadecylamine. Ozonolysis of these amines resulted in strong NO2 - and NO3 - ion signals that increased with the ozone exposure and suggested a mechanism of progressive oxidation. Additionally, a strong ion signal was detected for NO3 -(HNO3), which is the ion core of the most important ion cluster series in the troposphere, NO3 -(HNO3)n(H2O)m. PERCI-AMS was applied to the analysis of ozonized mixed particles of amines with oleic acid or dioctyl sebacate. In the ozonolysis of the amines with oleic acid, products included imines and amides. The routes to the amides were shown to most likely arise from the reactivity of stabilized Criegee intermediates and/or secondary ozonides with the amines. There was also direct evidence of the formation of a surface barrier in the octadecylamine and oleic acid reaction system, which resulted in the retention of oleic acid at high ozone exposures. These experiments have fostered a better understanding of the analytical capacity of PERCI-AMS in assaying the reactivity of organic aerosols as well as giving a more accurate description of the heterogeneous chemistry of these challenging reaction systems. Suggestions for adaptations to PERCI-AMS and future experiments on

Doctor of Philosophy / Department of Physics / Brett D. DePaola / Direct frequency comb spectroscopy (DFCS) is currently the highest resolution, absolute frequency spectroscopic technique known. In general, one does DFCS by scanning the repetition rate, f[subscript]r[subscript]e[subscript]p, of a comb laser and measuring fluorescence from the excited states of the specie under study. The technique has already been successfully characterized by a theoretical model that starts with the optical Bloch equations and, with a few simplifying assumptions converts them into linear coupled iterative equations. In the present work we build on that successful model to predict the characteristics of the ion yield from photoionization by the comb laser, as a function of f[subscript]r[subscript]e[subscript]p. We show that the ion spectrum yields the same atomic structure as the fluorescence spectra, but with greater efficiency. Here, we also set up an experiment and test this theory by measuring the ion signal from direct frequency comb spectroscopy. Furthermore, instead of actively controlling the frequency comb parameters, we allow them to drift, passively measuring them and the ion signal simultaneously. The experiments were found to be in agreement with theory, and the passive comb approach was found to be functional, though not as convenient as the conventional active comb.

Fong Wai-Yin Karen. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001 / Includes bibliographical references (p. 173-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Ever since its accidental discovery in the 70s, methylaluminoxane, MAO, has been a popular and widely used activator in olefin polymerization. Hydrolysis of primethylaluminum, Me3Al, produces MAO, an aluminum-, oxygen-, and methyl-containing oligomer. Polyolefins have become one of the most produced polymers, where MAO-activated single-site catalysts are responsible for the synthesis of polymers with highly defined structures. The detailed structure of MAO however, remains a mystery. In order to thoroughly understand the reactivity of MAO, knowing more about it is essential. Electrospray ionization mass spectrometry (ESI-MS) has proven to be a useful technique for studying catalysts and their activation chemistry. It has been shown that MAO is best thought of as a source for the highly reactive and Lewis acidic dimethylaluminum cation, [Me2Al]+. Synthetically, this ion is accessible via the reaction between trityl tetrakis(pentafluorophenyl)borate, [Ph3C]+[B(C6F5)4]- and trimethylaluminum, and this reaction was investigated in detail. A new reaction, substitution of H for CH3 onto the phenyl ring of the trityl carbocation, [Ph3C]+, was detected and found to be general for all trialkylaluminums studied. All instruments with detectors are prone to signal saturation at high concentration and mass spectrometers are no exception. Despite the advantages that ESI-MS offers, saturation can be one of the main obstacles in terms of the accurate quantification of species. This thesis tackles saturation issues in ESI-MS explicitly, because relatively high concentrations were necessary in order to keep unwanted decomposition reactions to a minimum. By detuning various parameters that allows troubleshooting this issue, data that better reflects the reality and the corresponding quantification of species is obtained. With the optimal settings of parameters, quantitative studies and the reactivity regarding the addition of trimethylaluminum, Me3Al, to the trityl carbocation [Ph3C]+ can be better understood. / Graduate

No description available.

by King Lai Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 86-93). / Title Page --- p.i / Table of Contents --- p.ii / List of Tables --- p.iv / List of Figures --- p.v / Abbreviations --- p.viii / Acknowledgements --- p.ix / Abstract --- p.x / Chapter CHAPTER ONE --- INTRODUCTION / Chapter 1.1. --- Mass Spectrometry for Macromolecular Analysis --- p.1 / Chapter 1.2. --- Laser Desorption --- p.3 / Chapter 1.3. --- Development of Matrix-assisted Laser Desorption/Ionization (MALDI) --- p.4 / Chapter 1.4. --- Matrix-assisted Laser Desorption/Ionization --- p.5 / Chapter 1.4.1. --- Laser --- p.6 / Chapter 1.4.2. --- Matrix Selection --- p.6 / Chapter 1.4.3. --- Sample Preparation Methodology --- p.7 / Chapter 1.4.4. --- Ion Formation Process(es) --- p.7 / Chapter 1.4.4.1. --- Desorption --- p.8 / Chapter 1.4.4.2. --- Ionization --- p.9 / Chapter 1.5. --- Time-of-Flight Mass Spectrometry --- p.12 / Chapter 1.6. --- Outline of the Present Work --- p.16 / Chapter CHAPTER TWO --- INSTRUMENTATION AND EXPERIMENTAL / Chapter 2.1. --- Instrumentation --- p.17 / Chapter 2.1.1. --- Laser System --- p.17 / Chapter 2.1.2. --- Ion Source --- p.19 / Chapter 2.1.3. --- Reflector --- p.20 / Chapter 2.1.4. --- Detector --- p.20 / Chapter 2.2. --- Experimental --- p.21 / Chapter 2.2.1. --- Synthesis of nitroanthracene-d9 --- p.21 / Chapter 2.2.2. --- Sample Preparation --- p.22 / Chapter CHAPTER THREE --- STUDIES OF THE EFFECTS OF SOLUTION pH / Chapter 3.1. --- Introduction --- p.25 / Chapter 3.2. --- Sample Preparation --- p.26 / Chapter 3.3. --- Results and Discussion --- p.28 / Chapter 3.3.1. --- Effect of Bronsted Base (NaOH) --- p.28 / Chapter 3.3.2. --- Effect of Lewis Base (Imidazole) --- p.33 / Chapter 3.3.3. --- Effect of Salt Concentration --- p.40 / Chapter 3.4. --- Conclusions --- p.44 / Chapter CHAPTER FOUR --- PROTON SOURCES FOR ION GENERATION IN MALDI-MS / Chapter 4.1. --- Introduction --- p.46 / Chapter 4.2. --- Sample Preparation --- p.47 / Chapter 4.3. --- Results and Discussion --- p.49 / Chapter 4.4. --- Conclusions --- p.55 / Chapter CHAPTER FIVE --- CATIONIZATION PROCESSES IN MALDI-MS : ATTACHMENT OF DIVALENT AND TRIVALENT METAL IONS / Chapter 5.1. --- Introduction --- p.57 / Chapter 5.2. --- Sample Preparation --- p.58 / Chapter 5.3. --- Results and Discussion --- p.60 / Chapter 5.3.1. --- Protonation versus Cationization --- p.60 / Chapter 5.3.2. --- Attachment of Divalent and Trivalent Metal Ions --- p.63 / Chapter 5.4. --- Conclusions --- p.80 / Chapter CHAPTER SIX --- CONCLUDING REMARKS --- p.82 / REFERENCES --- p.86

It is generally accepted that biological membranes consist of a lipid bilayer matrix with proteins incorporated into the lipid bilayer. Typically, these membranes are negatively charged due to the presence of negatively charged lipids in the bilayer as well as negatively charged molecular groups on proteins. Biologically active molecules, such as environmental pollutants, enter the membrane from the aqueous phase by adsorption or partitioning into the lipid bilayer. The thesis consists of two parts. Part I is a computational study of spatial distribution of electric potential in the aqueous portion of the membrane-water interface using two models of charge distribution: (i) the discrete charge model, in which charges are located on a square lattice either on the surface or embedded in the membrane: (ii) the continuous charge density (smeared charge), Gouy-Chapman, model in which the charge is assumed to be evenly spread on the membrane surface. The computed distributions of electric potential are used to predict spatial distributions of positively charged hexavalent cation of Ruthenium Red (RuR) at the membranewater interface. It was found that anomalous behavior of RuR cannot be explained by this version of the discrete charge theory. Part II is concerned with the distribution of ionized and un-ionized species of 2,4,6-Trichlorophenol (2,4,6-TrCP) in octanol-water system, which is often used as an experimental model for predicting the distribution of toxic chemicals in the environment. In this experimental study we obtained the pH dependence of the total distribution coefficient of 2,4,6-TrCP from which the octanol water partition coefficients of the un-ionized and ionized species were determined. We compared the octanol-water partition coefficient of several chlorophenols with experimental data on adsorption of ionized chlorophenols to lipid membranes. It was found that the membrane-water partition coefficient of ionized 2,4,6-TrCP is about 240 greater than that predicted from the octanol-water system. This finding supports the hypothesis that octanol-water partition coefficients cannot be used for predicting concentrations of ionized species of chlorophenols in lipid membranes.