Ce document présente une étude des mécanismes de relaxation de fullerènes induits par photoexcitation. Nous avons exploré les processus d'ionisation et de fragmentation de ces systèmes modèles suite à une irradiation par différentes sources de lumière : impulsion femtoseconde, laser à électron libre (IR lointain) et Synchrotron (XUV). Afin d'étudier ces mécanismes, nous utilisons l’imagerie par cartographie de vitesse qui nous permet de suivre l'évolution de la distribution angulaire de vitesse des particules émises. Suivant la durée, l'intensité et la longueur d'onde de l'excitation utilisée, la nature des mécanismes change drastiquement (mécanismes statistiques, ionisation cohérente en champ fort, autoionization de plasmons, etc…). Plusieurs approches théoriques sont utilisées allant du modèle Weisskopf pour les processus statistiques à la résolution de l'équation de Schrödinger dépendante du temps pour les processus cohérents. Cette étude permet de relier les mécanismes de relaxation intervenant à différentes échelles de temps / This document presents a study of relaxation mechanisms of fullerenes induced by photoexcitation. We have investigated ionization and fragmentation processes of these model systems under irradiation by various light sources: femtosecond pulse, free electron laser (far IR) and Synchrotron (XUV). To study these mechanisms, we use the velocity map imaging technique which allows us to follow the evolution of the angular distribution and velocity of the emitted particles. The nature of the relaxation mechanisms changes drastically (statistical mechanisms, coherent ionization in strong field, autoionization of plasmons, etc.) depending on the pulse duration, its intensity and the wavelength. Several theoretical approaches have been used including a Weisskopf modelling for the statistical processes and direct treatment of the time dependant Schrödinger equation for the coherent processes. This study allows us building bridges between the relaxation mechanisms occurring on various scales of time

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In occupational settings where rhodium is produced or used, such as the mining industry, refineries and catalytic industries, workers are at risk of being dermally exposed to this metal in either the metallic form or its salt compounds. A considerable amount of contradictory literature has been published with regard to the sensitising abilities of rhodium and no published information is available on the occupational dermal exposure of rhodium as well as its ability to permeate through the skin. Previous studies conducted on the in vitro permeation of metals, such as nickel, cobalt and chromium, have indicated that certain metals undergo oxidation in the presence of sweat and form ions which are able to permeate through skin. For some metals, this ionisation takes place more rapidly in an acidic environment and a decrease in the environmental pH would cause an increase in the release of ions from those metals. Aim: The aim of this study was to determine whether rhodium in the form of rhodium trichloride (RhCl3) would be able to permeate through the skin in vitro, as well as to determine whether any differences exist between the in vitro permeation of rhodium at a pH of 4.5 and a pH of 6.5. Methods: Full thickness abdominal skin was obtained as biological waste after surgery from Caucasian females ranging between 39 and 42 years of age. The Franz diffusion cell method was used in which the experimental cells contained synthetic sweat with RhCl3 and the blanks did not contain any RhCl3 in the donor compartment. All of the cells contained a physiological receptor solution in the receptor compartment. At intervals of 8, 12 and 24 hours, 2 ml of the receptor solution were removed for analysis. The receptor compartment was rinsed with 2 ml receptor solution which was also removed for analysis and 2 ml of fresh receptor solution was added to the compartment. After 24 hours, the receptor and donor solution was removed respectively for analysis and the skin was removed for digestion, prior to analysis. The mass of rhodium in the receptor solutions were determined using Inductively Coupled Plasma Mass Spectrometry. The donor solutions and digested skin solutions were analysed using Inductively Coupled Plasma Optical Emission Spectrometry. Results: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin with a cumulative increase in permeation over prolonged exposure time. After 8, 12 and 24 hours, the amount of rhodium that permeated through the skin was higher at pH 4.5 than for pH 6.5. After 12 hours, the permeation of rhodium was statistically significantly higher for pH 4.5 than for pH 6.5 (p = 0.02). At both pH values, the percentage of rhodium that accumulated in the skin was higher than the percentage of rhodium that diffused through the skin and the lag time was less than six hours. Conclusion: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin. A decrease in the pH of synthetic sweat led to an increase in the permeation of rhodium and it is recommended that future in vitro permeation studies be conducted at a pH of 4.5, as the skin surface pH of workers are generally considered to be below 5. A higher percentage of rhodium was retained in the skin than the percentage that diffused through, indicating the ability of rhodium to accumulate in the skin, from where it may exert health effects, such as sensitisation. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

In occupational settings where rhodium is produced or used, such as the mining industry, refineries and catalytic industries, workers are at risk of being dermally exposed to this metal in either the metallic form or its salt compounds. A considerable amount of contradictory literature has been published with regard to the sensitising abilities of rhodium and no published information is available on the occupational dermal exposure of rhodium as well as its ability to permeate through the skin. Previous studies conducted on the in vitro permeation of metals, such as nickel, cobalt and chromium, have indicated that certain metals undergo oxidation in the presence of sweat and form ions which are able to permeate through skin. For some metals, this ionisation takes place more rapidly in an acidic environment and a decrease in the environmental pH would cause an increase in the release of ions from those metals. Aim: The aim of this study was to determine whether rhodium in the form of rhodium trichloride (RhCl3) would be able to permeate through the skin in vitro, as well as to determine whether any differences exist between the in vitro permeation of rhodium at a pH of 4.5 and a pH of 6.5. Methods: Full thickness abdominal skin was obtained as biological waste after surgery from Caucasian females ranging between 39 and 42 years of age. The Franz diffusion cell method was used in which the experimental cells contained synthetic sweat with RhCl3 and the blanks did not contain any RhCl3 in the donor compartment. All of the cells contained a physiological receptor solution in the receptor compartment. At intervals of 8, 12 and 24 hours, 2 ml of the receptor solution were removed for analysis. The receptor compartment was rinsed with 2 ml receptor solution which was also removed for analysis and 2 ml of fresh receptor solution was added to the compartment. After 24 hours, the receptor and donor solution was removed respectively for analysis and the skin was removed for digestion, prior to analysis. The mass of rhodium in the receptor solutions were determined using Inductively Coupled Plasma Mass Spectrometry. The donor solutions and digested skin solutions were analysed using Inductively Coupled Plasma Optical Emission Spectrometry. Results: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin with a cumulative increase in permeation over prolonged exposure time. After 8, 12 and 24 hours, the amount of rhodium that permeated through the skin was higher at pH 4.5 than for pH 6.5. After 12 hours, the permeation of rhodium was statistically significantly higher for pH 4.5 than for pH 6.5 (p = 0.02). At both pH values, the percentage of rhodium that accumulated in the skin was higher than the percentage of rhodium that diffused through the skin and the lag time was less than six hours. Conclusion: At both pH values of 4.5 and 6.5, rhodium was able to permeate through the skin. A decrease in the pH of synthetic sweat led to an increase in the permeation of rhodium and it is recommended that future in vitro permeation studies be conducted at a pH of 4.5, as the skin surface pH of workers are generally considered to be below 5. A higher percentage of rhodium was retained in the skin than the percentage that diffused through, indicating the ability of rhodium to accumulate in the skin, from where it may exert health effects, such as sensitisation. / MSc (Occupational Hygiene), North-West University, Potchefstroom Campus, 2014

This thesis concerns the application of a new technique for measuring the stable isotopes of Sr, specifically pertaining to mass dependent fractionation in high temperature processes on the Earth and Moon. Processes such as mantle melting and differentiation on Earth and the formation of the Lunar Magma Ocean are investigated by the application of a double-spike TIMS method to terrestrial and lunar material to obtain high-precision ⁸⁷Sr/⁸⁶Sr, ⁸⁸Sr/⁸⁶Sr and ⁸⁴Sr/⁸⁶Sr data. Measurements of mantle-derived mafic material provide insights into the ⁸⁸Sr/⁸⁶Sr composition of the silicate mantle. Ocean Island Basalts possess restricted δ⁸⁸Sr compositions, whilst Mid-Ocean Ridge Basalts from the Pacific, Atlantic and Indian ridges reveal variations in δ⁸⁸Sr, the majority of which is seen within the FAMOUS section of the Mid-Atlantic Ridge. These variations are attributed partly due to the effects of plagioclase crystallisation and partly due to mantle source heterogeneity. Analyses of mineral separates from three different igneous systems provide an understanding of δ⁸⁸Sr fractionation at a mineral-scale. The possibility of δ⁸⁸Sr fractionation as a result of magmatic differentiation has also been assessed, and found to occur between the basalt and rhyolitic end-members of the Icelandic Hekla suite. Variations in the ⁸⁷Sr/⁸⁶Sr ratios of these rocks are also found, and considered most likely to be due to contamination. Analyses of lunar rocks indicate that the highland suite appears to be relatively uniform in δ⁸⁸Sr, whilst significant fractionation to light δ⁸⁸Sr compositions occurs in the mare basalts. Such variations are thought to be associated with the crystallisation of plagioclase during the differentiation of the lunar magma ocean. Lastly, precise ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr data yield a model age for the Moon of 4.523 ± 0.019 Ga.

Nous étudions la photoassociation dans un gaz d'hélium métastable 4He(23S1) ultrafroid piégé magnétiquement : des paires d'atomes en collision interagissent avec un ou deux champs laser pour former des molécules à purement longue portée 4He2(23S1-23P0), ou longue portée 4He2(23S1-23S1).<br />Des décalages lumineux dans la spectroscopie à un photon sont observés, et étudiés en fonction de l'intensité et la polarisation du laser de photoassociation, ainsi que l'état vibrationnel de la molécule photoassociée. Ils sont le résultat du couplage lumineux entre la molécule excitée et le continuum d'états de diffusion et les états liés de l'interaction entre deux atomes métastables. Leur analyse quantitative permet de déterminer la longueur de diffusion a=7.2 ± 0.6 nm caractéristique des collisions entre atomes métastables polarisés.<br />La photoassociation à deux photons est utilisée pour mettre en évidence des molécules 4He2(23S1-23S1) polarisées et de forte élongation. Celles-ci sont qualifiées d'exotiques, puisqu'elles sont constituées de deux atomes métastables, portant chacun une énergie interne de 20 eV suffisante pour ioniser l'autre. Les formes de raies obtenues par cette spectroscopie sont calculées et décomposées en sommes et produits en profils de Breit-Wigner et de Fano associés à des processus à un et deux photons. Leur ajustement aux données expérimentales permet de déterminer la durée de vie intrinsèque de la molécule tau=1.4±0.3 ms. Nous tentons d'interpréter cette durée de vie en terme d'autoionisation Penning induite par relaxation de spin. Nous montrons que cette hypothèse implique qu'il y ait un état quasi-lié proche de dissociation dans le potentiel d'interaction singulet entre atomes métastables pour rendre compte des expériences.

In this thesis we address fundamental questions about what constitutes and limits an HI disc, probing the distribution of neutral gas in the outer parts of galaxies. We use a subsample of galaxies observed as part of the THINGS survey to investigate the HI extent of spiral galaxy discs. We revisit previous work on the extent of HI discs, showing the limitations set by insufficient linear resolution. We then exploit the high spatial and velocity resolution combined with good sensitivity of THINGS to investigate where the atomic gas discs end and what might shape their edges. We find that the atomic gas surface density across most of the disc is constant at 5 – 10 x 10^20 atoms/cm^2 and drops sharply at large radius. The general shape of the HI distribution is well described by a Sérsic-type function with a slope index, n = 0.14 - 0.22 and characteristic radius ri. We propose a new column density threshold of 5 x 10^19 atoms/cm^2 to define the extent of the gas disc. This limit is well within reach of modern instruments and is at the level where disc gas becomes susceptible to ionisation by an extragalactic radiation field. We argue that at this level the HI column density has decreased to one tenth of that across the inner disc and that by going to yet lower column density the disc is unlikely to grow by more than 10% in radius. The HI column density at which the radial profiles turn over is too high for it to be caused by ionisation by an extragalactic UV field and we postulate that the HI extent is set by how galaxy discs form. Ionisation by extragalactic radiation will only play a rôle at column densities below 5 x 10^19 atoms/cm^2, if any. To study the crucial relation between observed edges and how closely these reproduce the intrinsic distribution of gas through our interferometric measurements, we created an ensemble of models based on four radial density distributions. We conclude that the observed edges in spiral galaxies faithfully reflect their intrinsic shape. Only in very specific cases of highly inclined (>75º) and/or large vertical scaleheight discs do we see strong deviations from the intrinsic surface density of the observed shape of the edges in spiral galaxies. In the case of NGC 3198 we concluded that there is no significant difference in the radial profiles obtained with either constant or exponentially increasing vertical gas distributions, when scaleheights are not higher than 1 kpc at the outskirts of the disc. We infer an upper limit to the scaleheight of NGC 3198 of 2 kpc. To address the distribution of neutral gas at larger scales, we study an HI rich, giant LSB galaxy, NGC 765. We present HI spectral line and radio-continuum VLA data, complemented by optical and Chandra X-ray maps. NGC 765 has the largest HI-to-optical ratio known to date of any spiral galaxy and one of the largest known HI discs in absolute size with a diameter of ~ 240 kpc measured at a surface density of 2 x 10^19 atoms/cm^2. We derive a total HI mass of M_HI = 4.7 x 10^10 M_sun, a dynamical mass of M_dyn = 5.1 x 10^11 M_sun and an HI mass to luminosity ratio of M_HI/L_B = 1.6, making it the nearest and largest “crouching giant”. Optical images reveal evidence of a central bar with tightly wound low-surface brightness spiral arms extending from it. Radio-continuum (L_1.4 GHz = 1.3 x 10^21 W/Hz) and X-ray (L_x ~ 1.7 x 10^40 erg/s) emission is found to coincide with the optical core of the galaxy, compatible with nuclear activity powered by a low-luminosity AGN. We may be dealing with a galaxy that has retained in its current morphology traces of its formation history. In fact, it may still be undergoing some accretion, as evidenced by the presence of HI clumps the size (< 10 kpc) and mass (10^8 -10^9 M_sun) of small (dIrr) galaxies in the outskirts of its HI disc and by the presence of two similarly sized companions. In an exploration of future work, we engaged in a study of the edges in the HI discs of dwarf irregular galaxies, their parameterisation and simulation. A collection of simulations were created based on the dwarf galaxy NGC 2366, similar to what was done for the larger spiral galaxies, showing that line-of-sight column densities are affected for discs with inclinations higher than 60º. Five out of eleven of the dwarfs from THINGS which are less inclined than 60º were analysed and parameterised with our Sérsic-type function. Their discs have average central column densities spread evenly from log_10 NHI = 20.7 atoms/cm^2 to log_10 NHI =21.3 atoms/cm^2. Their radial decline is shallower (slope index peaks around n ~ 0.3) than for spirals. The up-coming Local Irregular That Trace Local Extremes (LITTLE) THINGS project, will likely enlarge the number of local dwarf irregular (dIm) galaxies to which this type of analysis can be applied and for which these preliminary results verified.

The energy levels of a hydrogen Rydberg atom approaching a metallic structure are perturbed by the image-charge interaction with the surface. At small atom-surface separations surface ionisation of the Rydberg electron can occur, whereby the electron is transferred to a metal-localised state. In previous studies investigating surface ionisation at bulk metallic surfaces, this state has been part of a conduction band; however this thesis focuses on metallic and structured surfaces where the Rydberg electron transfers into a discrete image-state or hybrid 'well-image state'. The surface ionisation of hydrogen Rydberg atoms at a Cu(100) projected band-gap surface is investigated experimentally and theoretically. Experimentally, the surface ionisation of an incident beam of hydrogen Rydberg atoms is measured by extraction of the resulting ions. Resonance-enhanced charge transfer is seen for hydrogen Rydberg states that are degenerate with copper-localised image-states. A wavepacket propagation study shows that for on-resonance states the maximum in the surface-ionisation probability is shifted away from the surface by decreasing the collisional velocity. The discrete hybrid 'well-image states' localised along the surface normal of a thin-film change energy with thin-film thickness. The interaction of hydrogen Rydberg atoms with iron thin films deposited on an insulating substrate is investigated. The preference for electron penetration along the surface normal is seen by the resonance-enhancement of charge transfer at energies where the Rydberg state and well-image state are degenerate. By changing the thickness of the thin film, by in situ depositions, the energies of the well-image state are altered and the Rydberg n-values at which resonances occur, change. At a thickness of 30-monolayer the energetic spacings between the well-image states and the Rydberg states become comparable, and the single well-image state resolution is lost. A wavepacket-propagation study investigates the interaction of a nanoparticle and low-n hydrogen Rydberg atoms. The nanoparticle has a fully confined potential which at small radii yields well-spaced, fully discrete well-image states. Resonance-enhanced charge transfer occurs when the Rydberg state and the nanoparticle well-image state energy levels are degenerate. However, when there is poor energy matching between the nanoparticle well-image state and the Rydberg atom, no charge transfer is seen i.e. surface ionisation does not occur. Overall, the work presented here demonstrates the capability of Rydberg-surface studies to identify discrete, high-lying energy levels at specific surfaces.

Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature.

Am DLR Neustrelitz wird kontinuierlich die totale Ionosation der Atmosphäre bestimmt und globale Karten der vertikal integrierten Elektronendichte erstellt. Es werden dazu die Signale der Navigationssatelliten-Systeme GPS und GLONASS verwendet. In dieser Arbeit wird die Verteilung des totalen Elektronengehalt (TEC) oberhalb der mittleren Breiten während der Übergangssaison September bis November 2004 auf langperiodische Variationen im Bereich von mehreren Tagen sowie zonalen Wellenzahlen bis zu 5 untersucht. Die Ergebnisse werden mit einer Analyse von planetaren Wellen aus assimilierten Stratosphärendaten, Radardaten für Temperatur vom Collm Observatorium (51.3◦N, 13.0◦O) und Beobachtungen der kritischen Plasmafrequenz der F2-Schicht (f0F2) mit der Ionosonde in Juliusruh (54.6◦N, 13.4◦O) verglichen, um den meteorologischen Einfluss auf die Variation der Ionosphäre zu studieren. / The DLR Neustrelitz regularly produces maps of the total total electron content (TEC) on a global scale using the navigation satellite systems GPS and GLONASS to forecast space weather. In this study we turn our attention to the higher middle latitudes TEC variations during September to November 2004 in a long-period range of several days with a zonal wavenumber up to 5. The results are compared with a planetary wave analysis using assimilated stratospheric data, mesosphere/lower thermosphere radar temperature data at Collm observatory (51.3◦N, 13.0◦E) and the ionosonde observed critical plasma frequency of the F2-layer (f0F2) at Juliusruh (54.6◦N, 13.4◦E) to investigate the meteorological influences on ionospheric variability.