@phdthesis{Renziehausen2014,
  author    = {Renziehausen, Klaus},
  title     = {Wechselwirkung von Molek{\"u}len mit Laserpulsen: Untersuchungen zur numerischen Implementierung zeitabh{\"a}ngiger St{\"o}rungstheorie und zu Effekten der absoluten Phase von Laserpulsen beliebiger L{\"a}nge},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-100850},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In dieser Dissertation wurden zwei Aspekte der Wechselwirkung von Laserpulsen mit Molek{\"u}len betrachtet: Erstens wurden numerische Algorithmen, die auf der zeitabh{\"a}ngigen St{\"o}rungstheorie basieren, zur Berechnung von quantenmechanischen Wellenfunktionen analysiert. Zweitens wurden Effekte der absoluten Phase (Carrier envelope phase = CEP) von Laserpulsen bei der Laseranregung molekularer Systeme analysiert. In den Analysen zum ersten Aspekt wurden zwei verschiedene Algorithmen - in dieser Arbeit als simple und improved algorithm bezeichnet - verwendet, und die Normabweichung von mit diesen Algorithmen berechneten Wellenfunktionen untersucht. Es konnte gezeigt werden, dass diese Normabweichung f{\"u}r beide Algorithmen in zwei unterschiedliche Beitr{\"a}ge zerlegt werden kann. Der erste Normabweichungsbeitrag tritt aufgrund der numerischen Diskretisierung der Zeit auf und verschwindet, wenn der Zeitschritt, der die Dauer der Intervalle f{\"u}r diese Diskretisierung angibt, gegen Null geht. Man kann den ersten Normabweichungsbeitrag mit exzellenter Genauigkeit berechnen und seine Eigenschaften, die sich f{\"u}r die beiden Algorithmen erheblich unterschieden, eingehend analysieren. Der zweite Normabweichungsbeitrag tritt dadurch auf, dass die zeitabh{\"a}ngige St{\"o}rungstheorie nicht normerhaltend ist, und geht daher gegen Null, wenn die St{\"o}rungsordnung gegen unendlich geht. Dieser zweite Beitrag ist außerdem in guter N{\"a}herung unabh{\"a}ngig vom Zeitschritt und f{\"u}r beide Algorithmen n{\"a}herungsweise gleich. Des Weiteren kann man das Verhalten des zweiten Normabweichungsbeitrags im Gegensatz zum ersten Beitrag nur qualitativ beschreiben. F{\"u}r die Analyse zum zweiten Themengebiet dieser Arbeit, den CEP-Effekten, wurde betrachtet, ob CEP-Effekte auch f{\"u}r Laserpulse beliebiger L{\"a}nge auftreten k{\"o}nnen. {\"U}ber eine analytische Betrachtung erkennt man, dass dies f{\"u}r ein Zweiniveausystem nur dann der Fall ist, wenn beide Zust{\"a}nde vor Beginn der Wechselwirkung des Systems mit dem Laserpuls besetzt sind. Man kann aus diesem Ergebnis folgern, dass f{\"u}r einen Laserpuls, der zwei elektronische Zust{\"a}nde eines Molek{\"u}ls {\"u}ber Einphotonen{\"u}berg{\"a}nge koppelt, in der Regel kein CEP-Effekt f{\"u}r beliebige L{\"a}ngen dieses Pulses auftritt. Der Grund daf{\"u}r ist, dass vor der Wechselwirkung eines molekularen Systems mit einem Laserpuls f{\"u}r dieses {\"u}blicherweise nur der elektronische Grundzustand besetzt ist. In dieser Arbeit wird gezeigt, dass dieses Problem durch ein spezielles Zweipulsschema f{\"u}r die Anregung eines molekularen Systems gel{\"o}st werden kann. F{\"u}r dieses Pulsschema wird ein erster Puls verwendet, der zeitlich so kurz ist, dass Wellenpakete in mehreren elektronischen Zust{\"a}nden angeregt werden. Der nachfolgende zweite Laserpuls ist spektral schmal, und seine zeitliche L{\"a}nge kann beliebig groß gew{\"a}hlt werden. Man erh{\"a}lt f{\"u}r dieses Pulsschema Observablen, die von der CEP des zweiten Pulses, aber nicht von der CEP des ersten Pulses abh{\"a}ngen; somit ist ein CEP-Effekt nachweisbar. Derartige Observablen sind geometrische Asymmetrien f{\"u}r Zerfallsprodukte von Photodissoziationsreaktionen. Insbesondere unterscheidet sich das hier vorgestellte Pulsschema von anderen Zweipulsschemata, f{\"u}r welche Observablen von der Differenz der CEPs beider Pulse abh{\"a}ngen, aber nicht von der CEP einer der beiden Pulse allein.},
  subject      = {St{\"o}rungstheorie},
  language  = {de}
}
@phdthesis{Haeming2010,
  author    = {H{\"a}ming, Marc},
  title     = {Electronic Many-Body Effects in organic Thin-Films and Interfaces},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55494},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {The results of this thesis contribute to the understanding of the electronic properties of organic thin-films and interfaces. It is demonstrated that photoemission spectroscopy is very useful for studying surfaces and interfaces. Additionally it is shown, that many-body effects can be relevant for organic thin films, in particular at interfaces with strong interaction. These effects can have general implications for the material properties. In the first part of this thesis a systematic series of polyacene molecules is investigated with NEXAFS spectroscopy. The comparison of the data with core level and IPES data indicates that core excitations and core excitons need to be understood as many-body excitations. This finding implies for example that a high exciton binding energy is not necessarily associated with strong localization of the excited electron at the hole. As these effects apply also for valence excitons they can be relevant for the separation of charges and for the electron-hole recombination at interfaces. In the next chapter some fundamental effects in organic multilayer films and at organic-metal interfaces are studied with core level and NEXAFS spectroscopy. In this context a series of selected molecules is investigated, namely BTCDA, BTCDI, PTCDA and PTCDI. It is shown that in case of strong interface interaction a density of adsorbate-substrate states is formed which can lead to significant charge transfer satellites in the PES and NEXAFS spectra, similar to what is known for transition metal compounds. Moreover, it is demonstrated that the data can be modeled qualitatively by a basic approach which fuses the single impurity Anderson model with the description of charge transfer satellites by Sawatzky et al. This approach, which is equivalent to that of Gunnarsson and Sch{\"o}nhammer, allows even a relatively simple semi-quantitative analysis of the experimental data. The comparison of different adsorbate layers indicates that these many-body effects are particularly strong in case of partial occupation of the LUMO derived DOS. In the third part an organic multilayer film (SnPc), an organic-metal interface with strong coupling (SnPc/Ag) and an organic-organic interface (SnPc/PTCDA/Ag) are studied exemplarily with resonant Auger spectroscopy. The comparison of the data gives evidence for the contribution of many-body effects to the autoionization spectra. Furthermore, it is found that the electron-vibration coupling and the substrate-adsorbate charge transfer occurs on the time scale of the core hole life time. Moreover, the interaction at the organic-organic interface is weak, comparable to the intermolecular interaction in the multilayer films, despite a considerable rigid level shift for the SnPc layer. Furthermore, weak but significant electron-electron correlation is found for the molecular frontier orbitals, which are important for the substrate-adsorbate charge transfer. Therefore, these strongly coupled adsorbate films are briefly discussed within the context of the Hubbard model in the last part of this thesis. From the data derived in this work it can be estimated that such monolayer films are in the regime of medium correlations. Consequently one can expect for these adsorbate films properties which are related to the extraordinary behavior of strongly correlated materials, for which Mott metal-insulator transitions, sophisticated magnetic properties and superconductivity can be observed. Additionally some results from the investigation of alkyl/Si self-assembled monolayers are briefly discussed in the appendix. It is demonstrated exemplarily for the alkyl chains that the electronic band structure of short, finitely repeating units can be well modeled by a comparatively simple quantum well approach. In principle this approach can also be applied to higher dimensional systems, which makes it very useful for the description of E(k) relations in the regime of repeating units of intermediate length. Furthermore, the photoelectron and NEXAFS spectra indicate strong interaction at the alkyl/Si interface. It was found that the interface states can be modified by moderate x-ray irradiation, which changes the properties for charge transport through the SAM.},
  subject      = {Organischer Stoff},
  language  = {en}
}
@phdthesis{Matthaei2023,
  author    = {Matthaei, Christian Tobias},
  title     = {Studying the Photodissociation of Chlorine-Containing Molecules with Velocity Map Imaging},
  doi       = {10.25972/OPUS-32740},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-327405},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {The first is via direct dissociation and the second likely involves a barrier slowing down dissociation. Chlorine-containing hydrocarbons pose a great risk for the environment and especially for the atmosphere. In this thesis I present the photodissociation dynamics of multiple chlorine-containing molecules. The method of velocity map imaging was utilized for gaining information on the kinetic energy distribution of the fragments generated in the photodissociation reactions. First, the photodissociation of benzoyl chloride after excitation to the S1, S2 and the S3 state between 279 nm and 237 nm was studied. This stable molecule was an ideal candidate for demonstrating a new ionization scheme for chlorine atoms. It was shown that benzoyl chloride dissociates statistically from the ground state. Afterwards, the results from experiments on the radicals trichloromethyl and dichlorocarbene are presented in the range of 230 to 250 nm. These radicals remain after the dissociation of carbon tetrachloride and have not been studied in detail because of their instability. Trichlormethyl dissociates via two paths: The loss of a chlorine atom to dichlorocarbene and by decaying to CCl and a chlorine molecule. The dissociation to dichlorocarbene involves a barrier. If the photon exciting the molecule has enough energy to surpass the barrier, which is the case starting at around 235 nm, trichlormethyl dissociates rapidly resulting in an anisotropic VMI. However, if the the excitation energy is lower, the dissociation takes longer than a rotational period and the anisotropy is lost.The path to CCl is a statistical dissociation. Dichlorocarbene dissociates to CCl and Cl via to separate channels. The first is via direct dissociation and the second likely involves a barrier slowing down dissociation.},
  subject      = {Photodissoziation},
  language  = {en}
}