No description available.

No description available.

Naphthoxazine-spiro-indolines (NOSIs) can exist in a colourless and a coloured form. These compounds can interconvert between these two forms either photochemically or thermally and are resilient to degradation even after repeated cycles of colouration and bleaching. Absorption spectra of both the stable colourless form and the energetically less stable coloured form have been measured. Several NOSI compounds have been shown to photoconvert to the coloured form with an efficiency of between 0.06–0.74, depending upon the compound conditions under which the conversion is brought about. The factors which have been varied in this work are: the basicity of the 6'-substituent; the size of the N-alkyl group within these compounds; and the nature solvent or matrix in which the reaction occurs. Electron donation from the 6'-group has been shown to increase the quantum yield of the forward reaction whereas solvent polarity increases have been shown to reduce the quantum yield.

Studies have been carried out investigating the photochemical and photophysical properties of anthracene adsorbed on silica gel. The photochemistry and photo physics of anthracene in solution are well reported and known, hence its choice as a probe for the silica gel surface. UV -visible absorption and fluorescence spectra of anthracene adsorbed on silica gel reveal aggregate formation at very low loadings (1 % of a monolayer) indicating preferential adsorption occurs at some surface sites. Laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene, their production was found to be mono- and multi-photonic respectively. The decays of both these transients were complex and the rates increased with increasing loading. Analysis of the triplet state decay has been carried out by studying the delayed fluorescence which arises from triplet triplet annihilation. Fractal and twodimensional models have been used to describe this bimolecular decay. The coadsorption of anthracene and an electron donor having an oxidation potential below 1.09 V on silica gel causes electron transfer to occur from the electron donor to the anthracene radical cation produced following laser flash photolysis at 355 nm. Studies using a selection of electron donors with varying reduction potentials were carried out. The electron donor transfers an electron to the anthracene radical cation, thus greatly accelerating its rate of decay; for electron donors such as triphenylamine, N,N-dimethylaniline and N,N,N',N'tetramethyl- l,4-phenylenediamine the rise of the donor radical cation is observed as the anthracene cation decays. These systems were studied using fluorescence measurements and laser flash photolysis to study any fluorescence quenching and the rate of decay of both the anthracene triplet and radical cation. A selection of anthracene derivatives adsorbed onto silica gel were also briefly studied to see the effect of substituent group and its position. Symmetrically substituted dialkoxyanthracenes and 9-cyanoanthracene were used. The transient absorption spectra of the 2,3- and 2,6-dialkoxyderivatives and 9-cyanoanthracene revealed spectral similarities with that of unsubstituted anthracene. The spectra of9,10- and I,S-didecyloxyanthracene showed significant differences in the radical cation spectra to those obtained for unsubstituted anthracene.

Photoallergic compounds cause an allergy when applied to the skin and the skin is then exposed to light. Photoallergy is connected with the ability of the allergen to bind to the skin. This thesis describes much basic photochemistry of several photoallergens and has explained any differences in that photochemistry when on surfaces and in the presence of H.S.A.

Thermal conductivity is a crucial parameter for nuclear fuel, as it sets an upper limit on reactor operating temperature to have safety margins. Uranium mononitride (UN) is a prospective fuel for fast reactors, for which limited experimental studies have been conducted, compared to the currently dominating light-water reactor fuel, uranium dioxide. The aim of this thesis is to determine the thermal conductivity in UN and to determine its porosity dependence. This was done by manufacturing dense and porous high-purity samples of UN and examining them with laser flash analysis, which with data on specific heat and thermal expansion gives the thermal conductivity. To analyse the result, a theoretical study of the phenomenology of thermal conductivity as well as a review and comparison with previous investigations were carried out. The porosity range was 0.1–31% of theoretical density. Thermal diffusivity data from laser flash analysis, thermal expansion data and specific heat data was collected for 25–1400 C. The laser flash data had high discrepancy at higher temperatures due to thermal instability in the device and deviations due to graphite deposition on the samples, but the low temperature data should be reliable. As the specific heat data was also of poor quality, literature data was used instead. As for the thermal diffusivity data, the calculated thermal conductivity for lower temperatures are more accurate. A modified version of the porosity model by Ondracek and Schulz was used to analyse the porosity dependence of the thermal conductivity, taking into account the different impacts of open and closed porosity. / Värmeledningsförmåga är en avgörande egenskap för kärnbränslen, eftersom det begränsar den maximala drifttemperaturen i reaktorn för att ha säkerhetsmarginaler. Uranmononitrid (UN) är ett framtida bränsle för snabba reaktorer. Jämfört med det dominerande bränslet i lättvattenreaktorer, urandioxid, har endast begränsade experimentella studier gjorts av UN. Målet med detta arbete är att bestämma värmeledningsförmågan i UN och bestämma dess porositetsberoende. Detta gjordes genom att tillverka kompakta och porösa prover av UN och undersöka dem med laserblixtmetoden, vilket tillsammans med värmekapacitet och värmeutvidgning ger värmeledningsförmågan. För att analysera resultatet gjordes en teoretisk studie av värmeledning såväl som en genomgång av och jämförelse med tidigare undersökningar. Provernas porositet sträckte sig från 0.1% till 31% av teoretisk densitet. Värmediffusivitetsdata från laserblixtmetoden, värmeutvidgningsdata och värmekapacitetsdata samlades in för 25–1400 C. Värdena från laserblixtmätningen hade hög diskrepans vid höga temperaturer p.g.a. termisk instabilitet i anordningen och avvikelser p.g.a. grafitavlagring på proverna, men data för låga temperaturer borde vara tillförlitliga. Eftersom resultaten från värmekapacitetsmätningen var av dålig kvalité, användes litteraturdata istället. Som en konsekvens av bristerna i mätningen av värmediffusivitet är presenterade data för värmeledningsförmåga mest exakta för låga temperaturer. En modifierad version av Ondracek-Schulz porositetsmodell användes för att analysera värmeledningsförmågans porositetsberoende genom att ta hänsyn till olika inverkan av öppen och sluten porositet.

No description available.

No description available.

t-Butoxyl radical has been used as a chemical model for hydrogen abstractions in many enzymatic and biological systems. However, the question has arisen as to how well this reactive intermediate mimics these systems. In addressing this concern, absolute rate constants and Arrhenius parameters for hydrogen abstraction by t-butoxyl radical were measured for a broad class of substrates including amines, hydrocarbons, and alcohols using laser flash photolysis. Initially, no obvious reactivity relationship between rate constant and substrate structure was observed for these homolytic reactions. However, by closely examining the Arrhenius parameters for hydrogen abstraction, a pattern was revealed. For substrates with C-H bond dissociation energy (BDE) > 92 kcal/mole, activation energy increases with increasing BDE (as expected). However, for substrates with a lower BDE, the activation energy levels out at approximately 2 kcal/mole, essentially independent of structure. Viscosity studies with various solvents were conducted, ruling out the possibility of diffusion-controlled reactions. Entropy rather than enthalpy appears to be the dominating factor at 25°C, contributing to the free energy barrier for these reactions. Laser flash photolysis was also used to study radical anions. Using an indirect photoexcitation method, the properties of radical anions, generated from aryl ketones, were investigated. These radical anions, such as t-butyl phenyl ketone and cyclopropyl phenyl ketone, measured to have decay rate constants of 1.0 x 106 s-1, although they are known to be persistent when studied electrochemically. They also had measured activation energies around 6.0 kcal/mole and log A values close to 9.5. By extending the molecules's conjugation, the decay rate constants increased to greater than 107 s-1, decreased their activation energy by half, and lowered the log A values to 8.0. This trend was observed in aryl ketones such as trans-1-benzoyl-3-phenyl cyclopropane. It is believed that the generation of a benzyl radical during the decay that facilitates the enhancement of the unimolecular decays. These unimolecular decays were also observed with the previously studied hypersensitive SET probes, 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one. The decay rate constants for these radical anions were measured to be greater than 108 s-1, driven by the formation of an aromatic ring. / Ph. D.

Pulsed laser flash photolysis with both visible and infrared detection has been applied to the study of the displacement of weakly coordinating ligands (Lw) by strongly "trapping" nucleophiles (Ls) containing either an olefinic functionality (Ls = 1-hexene, 1-decene, 1-tetradecene) or nitrogen (Ls = acetonitrile, hydrocinnamonitrile) from the photogenerated 16 electron pentacarbonylchromium (0) intermediate. 5-Chloropent-l-ene (Cl-ol), a potentially bidentate ligand, has been shown to form (ol-Cl) pentacarbonylchromium (0), in which Cl-ol is bonded to Cr via a lone pair on the chlorine, and isomerize to (Cl-ol) pentacarbonylchromium (0), in which Cl-ol is bonded to the olefinic functionality on the submillisecond time scale. This process has been studied in both the infrared and visible region employing both fluorobenzene or n-heptane as the "inert" diluent. Parallel studies employing 1-chlorobutane and 1-hexene were also evaluated and showed great similiarity with the Cl-ol system. The data supported a largely dissociative process with a possibility of a small interchange process involving the H's on the alkyl chain. Studies were also carried out for various Cr(CO)6/arene/Ls systems (arene = various alkyl or halogenated substituted benzenes). The data indicated that for both C6H5R (R=various alkyl chains) or multi-alkyl substituted arenes (i.e. o-xylene, 1,2,3-trimethylbenzene) containing an "unhindered" ring-edge, bonding to the the Cr(CO)5 moiety occurs "edge on" via a partially delocalized center of unsaturation on the ring. The data indicated that both electronic and steric properties of the arenes influence the kinetics, and that an interchange pathway takes place at least, in part, through the alkyl chains on both the arenes and "trapping" nucleophiles. Moreover, halogenated arenes bond through the lone pair on the halogen for both CI- and Br- derivatives but "edge-on" for the fluorinated arenes. Finally, in the case of arene complexes without and "unhindered" ring-edge (i.e., 1,2,3,4,5-pentamethylbenzene) bonding can occur either "edge-on" or through the ring center of the arene or combination of the two. Carbonyl stretching frequencies for the arenes are also indicative of the type of bonding.