Density functional theory is used to calculate the core excitation spectra of titanium structures. Specifically, the core-hole approximation is used. In this scenario, the excitation energies of core electrons are calculated using the approximation that the core energy level be frozen throughout the relaxation process of the orbitals. This allows a more acurate determination of the resulting X-ray spectra. The method described has been implemented in an NWChem module.

Röntgen Freie Elektronen Laser ermöglichen es Doppel-K-Schalen Löchern in Molekülen in aufeinanderfolgenden mehrfachen Ionisationsschritten in bedeutender Anzahl zu erzeugen. Die Eigenschaften dieser zweifach ionisierten Zustände ist insbesondere relevant für die Strahlungsschäden bei Beugungsexperimenten mit kohärenter Röntgenstrahlung zur Bildgebung einzelner Moleküle. In dieser Arbeit wird der Auger Zerfall doppelt K-Schalen ionisierter Moleküle mittels quantenchemischer ab-initio Methoden untersucht. Zur Beschreibung des emittierten Auger Elektrons im kontinuierlichen Energiespektrum wird dabei die Ein-Zentrums Methode verwendet, in der die elektronische Wellenfunktion auf einem radialen Gitter beschrieben wird unter Verwendung von sphärischen Harmonischen. Wie anhand desWassermoleküls gezeigt wird, ergeben sich durch die Doppel-K-Loch induzierte Protonendynamik in dem Auger Spektrum ausgeprägte Flanken im höherenergetischen Teil jeder Spektralspitze. Die Lebensdauer von Doppel-K-Schalen Löchern in Molekülen ist deutlich verringert im Vergleich zu einfachen K-Löchern durch die K-Loch induzierten Abschirmeffekte der Valenzelektronen. Dieser Mechanismus wird durch ein einfaches Modell erklärt aus dem eine Beziehung zwischen Zerfallsrate und Valenzelektronenpopulation abgeleitet. Mögliche Konsequenzen dieser Ergebnisse für Röntgenbeugungsexperimente sind: Erstens, auch für Röntgenpulse kürzer als 10fs wird das Beugungsbild durch die K-Loch induzierten Umstrukturierungen der Valenzelektronen beeinflußt. Zweitens, die Gesamt-Ionisationsrate ist erhöht aufgrund der schnelleren Neubesetzung der K-Löcher.

Les propriétés de la matière peuvent être révélées en faisant interagir la matière avec la lumière. En particulier, les spectroscopies à rayons X sont largement utilisées pour étudier la structure électronique d'éléments isolés ou d'atomes et molécules dans un environnement donné, et sont spécifiques de la nature de l'élément. De telles capacités démontrent leur potentiel en terme d'analyse chimique. Le développement récent des lasers à électrons libres à rayons X (XFEL en anglais) permet de sonder la matière avec une résolution spatiale (angström) et temporelle (femtoseconde) hors de portée avec les lasers optiques et les sources synchrotron de troisième génération. Les caractéristiques uniques du rayonnement XFEL sont exploitées dans plusieurs domaines de recherche, comme la chimie, la physique et la biologie. En particulier, la spectroscopie de double trous a connu un nouvel essor avec l'apparition des XFELs. Les états double trous possèdent deux lacunes électroniques en couche interne. En régime XFEL, ces états sont produits principalement par l'absorption séquentielle de deux photons X d'une impulsion laser ultracourte (femtoseconde) et intense, avec la formation d'un état intermédiaire simplement ionisé. Au cours de cette thèse, nous avons étudié la formation de molécules doublement ionisées en couche de cœur, induite par l'absorption séquentielle de deux photons X d'une impulsion laser femtoseconde et intense. D'une part, nous mettons en évidence l'influence de la dynamique nucléaire sur les processus d'ionisation en couche de cœur. D'autre part, nous démontrons qu'un contrôle actif sur la compétition entre l'absorption de photon et le déclin Auger dans l'état intermédiaire simplement ionisé est possible en faisant varier la durée de l'impulsion laser. Afin d'atteindre ces objectifs, nous avons développé pour la première fois un modèle dépendant du temps et purement quantique, qui traite explicitement la dynamique nucléaire ainsi que l'absorption de photon, tandis que le déclin Auger est décrit de manière phénoménologique. Ce travail de recherche théorique ouvre la voie à une description complète de la formation de molécules doublement ionisées en couche de cœur en régime XFEL. / Properties of matter can be revealed through its interaction with light. In particular, X-ray based spectroscopies are widely used to gain insight into the local electronic structure of isolated elements or atoms or molecules embedded in an environment, and are element specific. Such capabilities evidence their potential as tools for chemical analysis. The recent development of X-ray free electron laser (XFEL) allows to probe matter with spatial (angström) and temporal (femtosecond) resolutions out of reach so far with optical lasers or third generation synchrotron sources. The unique characteristics of XFEL radiation are exploited in several areas, such as chemistry, physics and biology. In particular, double core hole spectroscopy, whose sensitivity is considerably enhanced compared to conventional X-ray spectroscopies, is on the rise. Double core hole states, also referred as hollow states, are characterized by two electron vacancies in the inner shell(s). In the XFEL regime, the dominant pathway to produce them is the sequential absorption of two x-ray photons, where a singly core ionized species is produced in the intermediate step. In the present thesis, we tackle the study of double core hole state formation induced by the sequential absorption of two x-ray photons from an intense femtosecond laser pulse. On one hand, we bring forward the influence of the nuclear dynamics on core photoionization processes. On the other hand, we demonstrate that an active control over the competition between photoabsorption and Auger decay in the intermediate single core hole state is possible by varying the laser pulse duration. In pursuing these goals, we develop for the first time a time-dependent full quantum model treating both the photon absorption and the nuclear dynamics explicitly as well as the Auger decay phenomenologically. This purely theoretical work paves the road for a complete description of molecular double core hole state formation in th XFEL regime.

No description available.

<p>Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects.</p><p>In this thesis, some atomic, molecular and cluster systems (clusters of O₂, CH₃Br, Ar/O₂, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using <i>ab initio</i> methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of <i>ab initio</i> and molecular dynamics (MD) methods.</p><p>Results on the dissociation behavior of CH₃Br and O₂ molecules in clusters are presented. The dissociation of the Na₂ molecule has been characterized and the molecular field splitting of the Na 2<i>p</i> level in the dimer has been measured. The molecular field splitting of the CH₃Br 3<i>d</i> level has been measured and the structure of CH₃Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O₂, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.</p>

Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects. In this thesis, some atomic, molecular and cluster systems (clusters of O2, CH3Br, Ar/O2, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using ab initio methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of ab initio and molecular dynamics (MD) methods. Results on the dissociation behavior of CH3Br and O2 molecules in clusters are presented. The dissociation of the Na2 molecule has been characterized and the molecular field splitting of the Na 2p level in the dimer has been measured. The molecular field splitting of the CH3Br 3d level has been measured and the structure of CH3Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O2, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.

Aqueous solutions were studied using photoelectron and Auger spectroscopy, based on synchrotron radiation and a liquid micro-jet setup. By varying the photon energy in photoelectron spectra, we depth profiled an aqueous tetrabutylammonium iodide (TBAI) solution. Assuming uniform angular emission from the core levels, we found that the TBA+ ions were oriented at the surface with the hydrophobic butyl arms sticking into the liquid. We investigated the association between ions and their neighbors in aqueous solutions by studying the electronic decay after core ionization. The (2p)−1 decay of solvated K+ and Ca2+ ions was studied. The main features in the investigated decay spectra corresponded to two-hole final states localized on the ions. The spectra also showed additional features, related to delocalized two-hole final states with vacancies on a cation and a neighboring water molecule. These two processes compete, and by comparing relative intensities and using the known rate for the localized decay, we determined the time-scale for the delocalized process for the two ions. We compared to delocalized electronic decay processes in Na+, Mg2+, and Al3+, and found that they were slower in K+ and Ca2+, due to different internal decay mechanisms of the ions, as well as external differences in the ion-solute distances and interactions. In the O 1s Auger spectra of aqueous metal halide solutions, we observed features related to delocalized two-hole final states with vacancies on a water molecule and a neighboring solvated anion. The relative intensity of these feature indicated that the strength of the interaction between the halide ions and water correlated with ionic size. The delocalized decay was also used to investigate contact ion pair formation in high concentrated potassium halide solutions, but no concrete evidence of contact ion pairs was observed. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 726