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Diese Dissertation präsentiert experimentelle Untersuchungen zu vertikalen und lateralen Strukturen von Polyelektrolytmultischichten (PEM) adsorbiert auf festen Oberflächen. Zur Herstellung von PEM werden Polykationen (Poly-(allylamin)hydrochlorid (PAH) oder Poly-(diallyldimethylammonium)chlorid, PDADMAC) und Polyanionen (Polys-(styren)sulfonat (PSS)) aus einer wässrigen Lösung auf eine hydrophile Siliziumdioxid-Oberfläche sequentiell adsorbiert. Um nicht–elektrostatische (sekundäre) Kräfte während der Adsorption zu untersuchen, wird Reichweite und Stärke der elektrostatischen Wechselwirkung durch eine definierte Konzentration monvalenten Salzes (c_ads) in den Polyelektrolyt (PE)-Lösungen eingestellt. Schichtdicke, und Homogenität der Multischichten entlang der PEM-Normalen werden mit Röntgenreflexion gemessen. Dies ist in Übereinstimmung mit veröffentlichten Daten und wird auf die elektrostatische Abschirmung, beschrieben durch die Debye-Hückel Theorie zurückgeführt. Komplementär wird Neutronenreflexion genutzt, um die Interpenetration einzelner Polyelektrolytschichten zu quantifizieren. Hierzu wird ein PEM aus zwei Blöcken unterschiedlicher Streulängendichte (SLD) hergestellt. Der SLD-Kontrast wird durch Verwendung von protonierten und deuterierten PSS realisiert. Durch Variation der Anzahl protonierter und deuterierter PE-Schichten wird die Breite der inneren Grenzflächen positionsabhängig entlang der PEM-Normalen vermessen. So ist erstmals eine eindeutige Bestimmung der Interpenetration (inneren Rauigkeit, sigma_int) benachbarter Polykat-/Polyananiondoppelschichten möglich. Die PEM-Dicke skaliert mit der Wurzel der Salzkonzentration in der Adsorptionslösung. Sowohl für PAH/PSS als auch für PDADMAC/PSS-Multischichten ist sigma_int nahe an der Film/Luft-Grenzfläche am geringsten und steigt mit zunehmendem Abstand. Für das PAH/PSS-System ist die Zunahme monoton, während beim PDADMAC/PSS-System sigma_int zunächst anwächst und sich dann eine konstante innere Rauigkeit (sigma_int, max) einstellt. Bei PADMAC/PSS steigt sigma_int,max mit zunehmendem c_ads. Erklärt wird diese Beobachtung durch eine höhere extrinsische Ladungsträgerkompensation der Polyelektrolytketten und eine verringerte elektrostatische Wechselwirkung, letzteres führt zu einer erhöhten Flexibilität der Polyelektrolytketten. Die Änderung von sigma_int wird über ein 1-dimensionales Diffusionsmodell quantifiziert. Zusätzlich wird der Polymerisationsgrad (Anzahl Monomere pro Kette) des Polykations variiert. Bei einer Vergrößerung des Polymerisationsgrades und großem c_ads nimmt die maximale innere Rauigkeit ebenfalls zu. Dies weist auf kooperative Effekte zwischen Polykat- und Polyanion hin, da nur das PSS deuteriert ist. Bei geeignetem c_ads nimmt die Dicke pro adsorbierter Polykation/Polyanion-Doppelschicht (d_Bl) zu. Während für den salzfreien Fall (c_ads = 0) die Parameter d_Bl und Polymerisationsgrad entkoppelt sind, wird die Kopplung mit steigendem c_ads immer deutlicher. Dies wird mit einer PE-Schicht erklärt, in der die PE-Ketten bei der Adsorption eine flache (c_ads = 0) bzw. geknäulte (c_ads > 0) Konformation einnehmen. In diesem Fall steigt sigma_int bei großem Polymerisationsgrad rapide nahe der PEM/Luft-Grenzfläche, d.h. die Diffusionskonstante wächst. An dieser Stelle wird die These aufgestellt, daß entropische Kräfte und Stressrelaxation die Interpenetration verursachen. sigma_int, max stellt einen metastabilen Gleichgewichtszustand dar. Da die Diffusionskonstante einer Kette invers mit der Anzahl der Segmente skaliert, erklärt Stressrelaxation warum die Diffusionskonstante mit steigendem Polymerisationsgrad zunimmt.
In this thesis, it was the subject to build a setup to study the interaction of clusters with intense laser light. A magnetron sputter cluster ion source was built to create metal clusters for the planned investigations. Furthermore, a linear Paul trap setup was built in order to allow the investigation of the mentioned interaction at one specific cluster size. The whole apparatus was characterized and first experiments were performed.
In this thesis, a stereoscopic camera system is presented that is designed for the use on parabolic flights for the investigation of dusty plasmas under microgravity conditions. This camera system consists of three synchronously triggered high-speed cameras observing a common volume of approximately (15 × 15 × 15) mm³ size. In this volume, the three-dimensional trajectories of a large number of particles surrounded by a dense dust cloud were reconstructed. For this task an intricate set of reconstruction algorithms has been developed, including a four-frame linking algorithm and a complex combined 2D/3D tracking algorithm for a reliable tracking of 3D particles. Furthermore, these algorithms effectively suppress so-called ghost particles in the evaluation process which are reconstructed from falsely identified 2D particle correspondences. Dusty plasmas under microgravity conditions are of special interest due to their complex structure and the variety of observable dynamic phenomena. Under typical discharge conditions, a central dust-free void is formed, surrounded by a dense particle cloud. Since the void is inherently dust-free, particles shot into the void can be uniquely identified and used to probe plasma properties inside this region. In the dust cloud itself, processes like self-excited dust-density waves can be observed under suitable experimental conditions. Using the presented camera setup and reconstruction algorithms, two parts of a dusty plasma under microgravity on parabolic flights are investigated. Initially, the force field creating and sustaining the central void is deduced and characterized. The combination of ion drag and electric field force is measured and compared to current models of the ion drag, showing a good agreement with these models. While previous investigations on the forces were limited to two-dimensional slices through the void, our measurements represent the first three-dimensional quantitative analysis of a large fraction of the void region. From this analysis the structure of the force field is determined and separated into a radial and a non-radial (or orthogonal) contribution. It is shown that the radial contribution dominates in the central void, while non-radial forces increase in magnitude close to the void edge. The radial domination is also observed in the velocity distribution of the probe particles which is significantly shifted to radially outward directed velocities for particles leaving the void. Assuming a strictly radial force profile in the horizontal mid-plane of the void, the friction coefficient determining the interaction of the probe particles with the neutral gas background is experimentally determined and shown to match the theoretical expectation. Subsequently, particles at the outer surface of the dust cloud are reconstructed. There, the particles are found to oscillate due to dust-density waves propagating through the high-density dust cloud. For the investigation of the correlation between waves and oscillating particles, the instantaneous wave and oscillation properties are determined and the instantaneous phase difference is obtained. Modeling the probe particles as driven, damped harmonic oscillators, these phase differences between waves and particles are interpreted with respect to the resonance frequency of the oscillating particles. Spatial variations of the phase difference are observed that may be attributed to different frequencies of the dust-density waves, or to changes of the resonance frequency induced by changing local plasma parameters. From a few measurements of particles oscillating at their resonance frequency, information about the surrounding plasma or properties of the particles themselves can be deduced. However, a larger number of reconstructed trajectories is necessary in order to interpret the phase differences on a reliable data basis. The presented camera setup in combination with the evaluation algorithms is a flexible system for the investigation of three-dimensional dusty plasmas. Its robust construction allows the operation of the system in challenging environments such as on parabolic flights, where spatial limitations and vibrations produced by the aircraft make special demands on such a diagnostic tool. This versatility makes our stereoscopic camera setup and the reconstruction process a suitable standard diagnostic for the application with dusty plasmas; this system will therefore be used in future research amongst other things for the investigation of boundary layers in extended three-dimensional dust clouds under microgravity.
In this thesis wave propagation in the whistler wave frequency range ωci≤ω≤ωce in the linear magnetized plasma experiment VINETA is investigated. The plasma is generated by a helicon antenna and has a diameter of about 10 cm. Whistler waves are launched by a loop antenna with a diameter of 4.5 cm and the fluctuating magnetic field is mapped by Ḃ-probes. Experiments are carried out for plasma parameters γ≤1/ √ 2 under which the only transversal polarized wave according to plane wave dispersion theory is the whistler wave. Due to the small collision frequencies ν≪1 cyclotron damping of whistler waves in this parameter regime is dominant and depends only on the electron plasma-β. The influence of the inhomogeneous plasma profile and excitation by a loop antenna is investigated by measurements of the fluctuating magnetic field perpendicular to the ambient magnetic field in azimuthal and radial axial planes. A mode characterized by the number of wave lengths m in the azimuthal direction is found. The mode structure is modified by the specific shape of the plasma density profile. Profiles with a homogeneous density inside the plasma radius are found to posses a comparably simple mode structure. An agreement in the mode structure of full-wave simulations in three dimensions, including a Gaussian density profile and excitation of the wave by a loop antenna, with the experimental results is found. Conclusions on the spatial structure of the excited mode are drawn using the simulations which predict excitation of an m=2 mode. The wave is found to be ducted within the plasma radius over a wide parameter range. A Helmholtz decomposition of the simulations electric field exhibits the fluctuating space charge as the dominant source for the electric field, while the contribution due to induction is negligible. The magnetic field is given partially by the electron and displacement current. Both contributions to the magnetic field are of the same order of magnitude. The frequency dependency of the excited modes spatial damping increment is investigated using measurements of the magnetic fluctuations along the symmetry axis of the plasma. In order to illustrate the parameter dependency, the electron plasma-β is varied over two orders in magnitude in the range β = 4·10-4 - 2.4·10-2. The experimental result for the spatial damping increment of the mode yields a strong damping for wave frequencies ω/ωce > 0.5 at maximum plasma-β, which shifts to higher frequencies with decreasing β. The parameter dependency of the damping for a fixed frequency is studied in an axial ambient magnetic field gradient. In both cases an excellent agreement between the experimental result and predictions for cyclotron damping from plane wave dispersion theory is found.
Computational chemical physics can give important input to astrophysical modelling and other fields of physics, where molecular properties are of importance. Understanding of spectroscopic and reactive behaviour is crucial for many systems of astrophysical interests like stars, interstellar medium and comets. Especially stellar atmospheres are of interest, because the complex physics of stars are not yet completely understood. Stars are in an unstable balance of gravitation and radiation pressure and the atmospheric dynamics have been subject of extensive modelling. Complete and accurate spectroscopic information of the atoms and molecules in these atmospheres is necessary for this attempt. In addition, the only information we have about astrophysical systems is light which is emitted or absorbed by particles in these media. This is not only true for astrophysics. In plasma physics sometimes the usage of invasive diagnostics, like Langmuir probes, is not wanted because they disturb the system. In these cases some information of the system can be regained by passively measuring infrared spectra of the plasma or by active induction of electronic transition like the laser-induced fluorescence method. Another remote sensing application is the measurement of the atmospheric composition on earth. Here, larger particles in the atmosphere as well as greenhouse gases are of current interest. Unfortunately, the experimental spectroscopic data, which is needed for the understanding and interpretation of the measured spectra, is often incomplete. This gap can be, to some extend, filled by computational chemical physics. The aim of this work was to investigate the capabilities and limitations of ab initio based potential energy surfaces for spectroscopic and reactive studies and to apply these methods to problems of rovibrational and rovibronic spectroscopy and reaction dynamics. The choice of ab initio methods and the potential fitting methods is critical for the computational chemical physics, as all further quantities directly depend on their quality. In this work modified versions of the Braams polynomial potential energy surface were used. A high level coupled cluster ab initio method was used to build potentials for a series of small hydrocarbons. Hydrocarbons can be found almost everywhere on earth and in the universe. They exist in laboratory plasmas, stellar and planetary atmospheres and interstellar gases. In all these cases, light emitted or absorbed by the molecules is an important diagnostics of the system. The potential constructed in this work partly included a cluster expansion, which adds reactant configuration spaces to the fits. This could not be done for CH_3 and higher hydrocarbons, because of the limitations of the Coupled Cluster ab initio method, which is well suited for the potential wells, but not for the dissociation regions. The examples of methyl and methane show how the potentials can be used for rovibrational spectroscopy. Results of radiation transport simulations illustrate the importance of as complete-as-possible line lists for radiation transport calculations.\\ The rovibronic spectroscopy of diatomic molecules is another important aspect for the stellar atmospheric modelling. Metal hydrides and oxides add opacity to the atmosphere in the visible light and ultraviolet frequency regions, as well as do the hydrocarbons in the infrared one. In addition the spectra of metal hydrides/oxides can be used to gather information about metal and their isotope abundances. They are used as markers for the conditions in the atmospheres of stars. In this work a new code was developed, that efficiently calculates bound-bound transitions between electronic states and bound-continuum cross sections for diatomic molecules. It also offers an adequate treatment of quasi-bound rovibrational states. One important representative of the diatoms is magnesium hydride, MgH. Before this work, line lists and photodissociation cross section were available involving the three lowest doublet states of MgH. In this work new potential energy curves were calculated and adapted to updated experimental data. This causes changes in the relative energies between the electronic states and therefore shifts in the line lists. These are important, because accurate line positions are needed for the identification of spectral lines. In addition two further electronic states were included in the calculations. This expands the spectral range of MgH into the near ultraviolet region. Radiation transport models showed significant absorption by MgH from the newly added electronic states. A second usage of the diatomic potential energy curves are photodissociation cross sections. As interstellar environments are chemically active, such data is necessary for a complete picture of the ongoing processes. The photodissociation cross sections of MgH reveal a stronger dependence of the underlying potential than the bound-bound lines. In the case of MgH the cross sections are rather weak, besides occasional resonance lines which can be several orders of magnitude stronger. As mentioned, not only spectroscopic, but also reactive behaviour of molecules is important in astrophysics. A current problem connected with this is the abundance of CH^+ in interstellar clouds. Its measured abundances do not fit the predictions from theoretical models. In addition Gerlich and co-workers recently measured low temperature H + CH^+ -> C^+ + H_2 reaction rates, which diverge from the theoretical picture and which could not be explained. In this work a reactive potential energy surface was built for the CH_2^+ system, which was then used to perform extensive calculations with quasi-classical trajectory and quantum scattering methods. It was found out, that the potentials used in previous works are not accurate enough to allow low temperature calculations. Results from these potentials must be taken with care. Furthermore, the results from the new potential energy surface indicate significantly reduced reaction rates compared to previous numerical studies. This is in agreement with the new results of Gerlich and co-workers. Nevertheless, the large error bars in the low temperature range for experimental as well as numerical results strongly suggest refined methods to be developed for both, before a final conclusion can be made. This work demonstrated the possibility of modern computational chemical physics to supply consistent data for spectroscopy and reaction dynamics. These are necessary and important inputs for fields like astrophysics, plasma physics and chemistry.