Neste trabalho, descrevemos os conceitos de alinhamento e orientação baseados no formalismo de Fano e Macek e estudamos a fotoionização do estado fundamental do átomo de Hélio. Para isso usou-se uma função de onda aproximada obtida a partir da diagonalização do operador de Gailitis- Damburg. A anisotropia do sistema formado após a colisão foi caracterizada através do cálculo da densidade eletrônica do íon e através do tensor de alinhamento e do vetor de orientação. O comportamento destes parâmetros para as transições n? -> 1s e n->n-1 em função de n (número quântico principal do íon) foi graficado para as duas simetrias relevantes, 1P° e 3P°. Observamos que o alinhamento máximo do sistema, em relação ao eixo de maior simetria definido como sendo o eixo z ocorre no limite de Wannier (n-> ?). Nesta situação o elétron iônico se encontra ao longo do eixo z para a simetria 3 P° e perpendicular ao eixo z para a simetria 1 P°. Esse fenômeno é causado pela interação elétron-elétron / In this work we describe the concepts of aligrnment and orientation based on the formalism of Fano and Macek formalism and we study the photoionization of the Helium atom ground state. We have used an approximate wave function obtained from the diagonalization of the Gailitis- Damburg operator. The anisotropy of the system formed after the colision was measured through the calculation of the ion electronic density and also by the use of the alignment tensor and orientation vector. The behaviour of these parameters for the transitions np ->1s and n ->n-1 as a function of n (the principal quantum number of the ion) was plotted for both the relevant symmetries, 1 P° and 3 P°. We have observed that the maximum alignment of the system, with respect to the dominant symmetry axis defined as the z axis, occurs in the Wannier threshold (n->?). This leads to the alignment of the ionic electron along the z axis for the 3 P°symmetry, and orthogonal to the z axis for the 1P° symmetry. This phenomenom is caused by the electron-electron Ínteraction.

Abstract In this thesis, the electronic structure of selected atoms was investigated by means of electron and uorescence spectroscopy. Synchrotron radiation was used to excitate atoms in gas phase. In particular, the photoionization and subsequent Auger decay processes in metal vapours were studied as well as the resonant Auger decay in rare gases. The experimental results were analyzed together with theoretical predictions obtained utilizing the multiconfiguration Dirac-Fock method.

archives@tulane.edu / A cold molecular beam approach has been pioneered to investigate the pyrolysis reactions of triglycerides (TGs) as a function of temperature. Traditionally, an established repertoire of laser techniques is utilized for multiple species present, which has been extensively used for a detailed study of specifically targeted species that are often novel and reactive. Instead, we have applied these methods for the mass characterization of numerous product species as they appeared. Unlike traditional batch reactor studies of pyrolysis, where terminal products are identified and characterized generally using GC/MS methods, herein, product analysis was conducted in real time. Experiments were performed by recording mass spectra as a function of increasing sample temperature. For clearer results and interpretation, most studies employed model TGs containing a single fatty acid, such as oleic or stearic acid. Soft photoionization was conducted using 118 and 266 nm laser-based pulses. Time-of-flight mass spectroscopy (TOF-MS) was conducted after each photoionization pulse. Several novel direct observations include 1) the observation of initial cracking temperatures and the formation of non-aromatic and aromatic products; 2) the determination of key factors for pyrolysis—fatty acid detachment from the glycerol backbone and subsequent fatty acid pyrolysis; 3) the growth of C6 and C7 fragments as an important precursor for following association reactions. The use of 266 nm pulses exclusively facilitated the sensitive and selective photoionization of aromatic products and, thus, the thorough examination of the evolving aromatic products. Unlike the batch reactor studies of terminal products, the molecular beam studies of aromatic products revealed the evolution to a small number of selective and relatively massive polycyclic aromatic hydrocarbons (PAH). It is deduced that in a batch reactor, these undetected products ultimately lead to solids and tars that are difficult to analyze. Our investigation revealed that hydrogen addition showed some effectiveness in inhibiting formation of large / 1 / Ibrahi M. Alhroob

No description available.

A simple model for above threshold ionization is presented in this work. It is based on modeling the pulsed laser beam involved in ionization as a cylinder consisting of elementary cells whose volumes are very small compared to the pulse volume. A cell is occupied by a number of photons determined probabilistically and found to follow the Poisson distribution. During ionization, resulting from the application of the laser field, a typical atom finds itself in one of the cells and one of its electrons absorbs the photon energy. The electron will be detached from its atom and will exit the interaction volume (the laser beam) if the energy contained in the particular cell is high enough. The model predicts all possible energies of the electrons exiting the beam and produces energy spectra associated with these electrons. While most of the other available models make only qualitative comparisons, we are able to make both qualitative and quantitative comparisons with experimental data. / Master of Science

Call number: LD2668 .T4 1985 T36 / Master of Science

No description available.

Doctor of Philosophy / Department of Physics / Chii-Dong Lin / Isolated attosecond pulse (IAP) is a tool of probing electronic dynamics occurring in atoms, molecules, clusters and solids, since the time scale of electronic motion is on the order of attoseconds. The generation, characterization and applications of IAPs has become one of the fast frontiers of laser experiments. This dissertation focuses on several aspects of attosecond physics. First, we study the driving wavelength scaling of the yield of high-order harmonic generation (HHG) by applying the quantum orbit theory. The unfavorable scaling law especially for the short quantum orbit is of great importance to attoseond pulse generation toward hundreds of eVs or keV photon energy region by mid-infrared (mid-IR) lasers. Second, we investigate the accuracy of the current frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) and phase retrieval by omega oscillation filtering (PROOF) methods for IAP characterization by simulating the experimental data by theoretical calculation. This calibration is critical but has not been carefully carried out before. We also present an improved method, namely the swPROOF which is more universal and robust than the original PROOF method. Third, we investigate the controversial topic of photoionization time delay. We find the limitation of the FROG-CRAB method which has been used to extract the photoionization time delay between the 2s and 2p channels in neon. The time delay retrieval is sensitive to the attochirp of the XUV pulse, which may lead to discrepancies between experiment and theory. A new fitting method is proposed in order to overcome the limitations of FROG-CRAB. Finally, IAPs are used to probe the dynamic of electron correlation in helium atom by means of attosecond transient absorption spectroscopy. The agreement between the measurement and our analytical model verifies the observation of time-dependent build up of the 2s2p Fano resonance.

A presente pesquisa trata de calibrar, a ferir e utiliza em laboratório um detetor de fotoionização (método de campo) proveitoso na caracterização de áreas contaminadas por vazamentos de gasolina; comparar as informações do detetor com os resultados obtidos com balança analítica; comparar os resultados de fluxo de massa medido com o previsto pelo modelo JURY contido no software APIDSS 2.0 O detetor mostrou-se útil como primeira ferramenta na caracterização de áreas contaminadas recentemente (até 100 dias). Para áreas onde a contaminação esteja em uma fase mais avançada o aparelho mostrou-se útil na detecção de alterações; os modelos desenvolvidos com base nos resultados obtido com balança e com o detetor de fotoinização apresentaram resultados satisfatórios para o período de ensaio; as comparações realizadas com o software APIDSS 2.0 serviram para a confirmação dos resultados obtidos. / The present research aims at gauging, checking and using a photoionization detector (field method) in laboratory advantageous to the characterization of areas polluted by leaks of gasoline; to compare the information of the detector with the results obtained in the analytic scale; to compare the results of the measured mass flow with those foreseen by the model JURY of the software APIDSS 2.0. The detector showed to be useful as a first tool in the characterization of areas recently contaminated (up to 100 days). To areas where the contamination is in a more advanced phase, the apparel showed to be useful in the detection of alterations; the development of models based on the results obtained with a scale and with the photoionization detector presented satisfactory results for the rehearsal period; the comparisons accomplished by the software APIDSS 2.0 confirmed the obtained results.

O presente trabalho propõe-se a mapear espacialmente as propriedades físicas de um conjunto destes objetos, de morfologia bipolar, e então efetuar sua modelagem. Para este mapeamento foram executadas observações do Observatório Pico dos Dias (LNA/MCT) através das técnicas observacionais de espectroscopia de fenda longa e de campo integral. As modelagens foram executadas com o código de fotoionização CLOUDY em seu formato pseudo tridimensional, CLOUDY_3D. Nossos resultados mostram que as simulações são capazes de reproduzir em boa medida o quadro de observações realizadas, mesmo partindo de considerações simplificadoras para a construção do ambiente astrofísico analisado. Como produto, estabelece-se limites para os parâmetros dos objetos, tais como características da distribuição de matéria, propriedades da fonte central, distância e dimensões envolvidas. / This study aims to map spatially the physical properties of a set of objects, with bipolar morphology, and then build their models. For this mapping, observations were performed at the Pico dos Dias Observatory (LNA / MCT) using the observational techniques of long slit and integral field spectroscopy. Modeling was performed with the photoionization code CLOUDY in its pseudo three-dimensional format, CLOUDY_3D. Our results show that the simulations are able to reproduce the major features of observations, even taking simplifying assumptions for the astrophysical environment analyzed. As a product, it establishes limits for the parameters of objects, such as characteristics for the distribution of matter, properties of the central star, distances and related dimensions.