No description available.

Die Entwicklung Freier-Elektronen-Laser und einer neuen Generation von Strahlungsquellen erlaubt die Realisierung hoher Intensitäten und kurzer Pulsdauern. Im Regime niedriger Laserintensitäten war bisher die Dipolnäherung recht erfolgreich bei der Beschreibung der durch die Licht-Materie-Wechselwirkung erzeugten Dynamik, wodurch viele experimentell beobachtete Resultate reproduziert werden konnten. Bei den durch die neuen Strahlungsqullen erzeugten bisher unerreichten Intensitäten und Rönten-Wellenlängen kann die Dipolnäherung allerdings zusammenbrechen. Höhere Multipol-Wechselwirkungen, die mit dem Strahlungsdruck assoziiert werden, sollten dann erwartungsgemäß wichtig zur genauen Beschreibung der Wechselwirkungsdynamiken werden. In dieser Arbeit wird eine Methode zur Lösung der nichtrelativistischen zeitabhängigen Schrödingergleichung zur Beschreibung von Systemen mit einem einzelnen aktiven Elektron, das mit einem Laserfeld wechselwirkt, über die Dipolnäherung hinausgehend erweitert. Dabei wird sowohl die Taylor- als auch die Rayleight-Multipolentwicklung des Retardierungsterms ebener Wellen verwendet. Es wird erwartet, dass die Berücksichtigung höherer Ordnungen der Multipolwechselwirkung zu einer erhöhten Genauigkeit und Richtigkeit der Resultate führen. Weiterhin wird gezeigt, dass die Rayleigh-Multipolentwicklung für gleiche Laserparameter genauer ist und schneller zur Konvergenz der numerischen Rechnung führt. Die nicht-Dipoleffekte spiegeln is sowohl in den differentiellen als auch den totalen Ionisierungswahrscheinlichkeiten in Form von erhöhten Ionisierungsausbeuten, verzerrten ATI Strukturen und einer Asymmetrie in der Photoelektronenwinkelverteilung in der Polarisations und Propagationsrichtung wider. Es wird beobachtet, dass die nicht-Dipoleffekte mit der Intensität, Wellenlänge und Pulsdauer zunehmen. Es werden Ergebnisse sowohl für das Wasserstoffatom als auch das Heliumatom gezeigt. / The development of free-electron lasers and new generation light sources is enabling the realisation of high intensities and short pulse durations. In the weak-field intensity regime, the electric dipole approximation has been quite successful in describing the light-matter interaction dynamics reproducing many of the experimentally observed features. But at the unprecedented intensities and x-ray wavelengths produced by the new light sources, the electric dipole approximation is likely to break down. The role of higher multipole-order terms in the interaction Hamiltonian, associated with the radiation pressure, is then expected to become important in the accurate description of the interaction dynamics. This study extends the solution of the non-relativistic time dependent Schrödinger equation for a single active electron system interacting with short intense laser pulses beyond the standard dipole approximation. This is realized using both the Taylor and the Rayleigh plane-wave multipole expansion series of the spatial retardation term. The inclusion of higher multipole-order terms of the interaction is expected to increase the validity and accuracy of the calculated observables relative to the experimental measurements. In addition, it is shown that for equivalent laser parameters the Rayleigh multipole expansion series is more accurate and efficient in numerical convergence. The investigated non-dipole effects manifest in both differential and total ionization probabilities in form of the increased ion yields, the distorted above-threshold-ionization structure, and asymmetry of the photoelectron angular distribution in both polarization and propagation directions. The non-dipole effects are seen to increase with intensity, wavelength, and pulse duration. The results for hydrogen as well as helium atom are presented in this study.

After giving a brief background on the subject we introduce in section two the Phase-Integral Method of Fröman & Fröman in terms of the platform function of Yngve and Thidé. In section three we derive a different form of the radial Bohr-Sommerfeld condition in terms of the apsidal angle of the corresponding classical motion. Using the derived expression, we then show how easily one can calculate the exact energy eigenvalues of the hydrogen atom and the isotropic three-dimensional harmonic oscillator, we also derive an expression for higher order quantization condition. In section four we derive an expression for the angular frequencies of a restricted (0≤φ≤β) soap bubble and also give a proposition concerning the parameters l and m of the associated Legendre differential equation. / Vi använder Fröman & Frömans Fas-Integral Metod tillsammans med Yngve & Thidés plattformfunktion för att härleda kvantiseringsvilkoret för högre ordningar. I sektion tre skriver vi Bohr-Sommerfelds kvantiseringsvillkor på ett annorlunda sätt med hjälp av den så kallade apsidvinkeln (definierad i samma sektion) för motsvarande klassiska rörelse, vi visar också hur mycket detta underlättar beräkningar av energiegenvärden för väteatomen och den isotropa tredimensionella harmoniska oscillatorn. I sektion fyra tittar vi på en såpbubbla begränsad till området 0≤φ≤β för vilket vi härleder ett uttryck för dess (vinkel)egenfrekvenser. Här ger vi också en proposition angående parametrarna l och m tillhörande den associerade Legendreekvationen.

This thesis primarily focuses on the electrochemical properties of the H₂/H⁺ redox couple, at various metallic electrodes in room temperature ionic liquids. Initially, a comprehensive overview of room temperature ionic liquids, RTILs, compared to conventional organic solvents is presented which identifies their favourable properties and applications, followed by a second chapter describing the basic theory of electrochemistry. A third chapter presents the general experimental reagents, instruments and measurements used in this thesis. The results presented in this thesis are summarized in six further chapters and shown as follows. (1) Hydrogenolysis, hydrogen loaded palladium electrodes by electrolysis of H[NTf₂] in a RTIL [C₂mim][NTf₂]. (2) Palladium nanoparticle-modified carbon nanotubes for electrochemical hydrogenolysis in RTILs. (3) Electrochemistry of hydrogen in the RTIL [C₂mim][NTf₂]: dissolved hydrogen lubricates diffusional transport. (4) The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends. (5) The formal potentials and electrode kinetics of the proton_hydrogen couple in various room temperature ionic liquids. (6) The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a Platinum microelectrode in room temperature ionic liquids. The first two studies show electrochemically formed adsorbed H atoms at a metallic Pt or Pd surface can be used for clean, efficient, safe electrochemical hydrogenolysis of organic compounds in RTIL media. The next study shows the physicochemical changes of RTIL properties, arising from dissolved hydrogen gas. The last three studies looked at the electrochemical properties of H₂/H⁺ redox couple at various metallic electrodes over a range of RTILs vs a stable Ag/Ag⁺ reference couple, using H[NTf₂] and benzoic acid as proton sources. The kinetic and thermodynamic mechanisms of some reactions or processes are the same in RTILs as in conventional organic or aqueous solvents, but other remarkably different behaviours are presented. Most importantly significant constants are seen for platinum, gold and molybdenum electrodes in term of the mechanism of proton reduction to form hydrogen.