Nous étudions dans ce mémoire de thèse les états diexcités 1po de l'atome d'hélium, situés au voisinage de son seuil de double ionisation (79 eV), atteints par absorption d'un photon. Ces états diexcités sont soit les états du double continuum situés au-dessus du seuil de double ionisation soit les états doublements excités situés en dessous. Ces deux types d'états diexcités sont dégénérés aux états du continuum simple avec ou sans excitation de l'ion résiduel He+ et sont donc fortement couplés à ces derniers. Dans un processus de photoabsorption à un photon, ces états ne peuvent être accessibles que grâce aux corrélations électroniques du système. Le travail que nous avons réalisé s'inscrit dans une démarche qui vise à étudier tous ces états par une seule et même méthode contrairement aux travaux antérieurs où les méthodes se spécialisaient dans le traitement d'un seul type d'état.<br />Nous utilisons pour cela la méthode HRM-SOW (Hyperspherical R-Matrix with Semiclassical Outgoing Waves), initialement dédiée à l'étude du double continuum de He.<br />Dans ce travail, elle est étendue à la description du continuum simple avec ou sans excitation. Ainsi, nous avons pu calculer les sections efficaces de photoionisation simple avec ou sans excitation jusqu'à n=50 de He à 100meV seulement au dessous de son seuil de double ionisation. Une analyse détaillée en ondes partielles a permis de mettre en évidence le rôle des corrélation angulaires et radiales dans les états du simple continuum de He. Nous avons ensuite établi une relation de continuité entre la photoionisation double et la photoionisation simple avec une excitation infinie de l'ion résiduel He+. la méthode HRM-SOW permet également de calculer la section efficace intégrée de double photoionisation avec une grande précision y compris à très basse énergie. Nous l'avons donc appliquée pour différentes énergies de photon au voisinage du seuil afin de tester la loi de seuil de Wannier. Les résultats obtenus sont en accord d'une part avec les prédictions théoriques de Wannier, d'autre part avec les résultats expérimentaux. La méthode HRM-SOW apparaît donc comme une méthode complète au dessus du seuil de double ionisation. <br />Nous avons poursuivi ce travail en amorçant l'étude des états doublement excités autoionisants. Ceux ci se manifestent comme des résonances dans les sections efficaces d'ionisation sous le seuil de double ionisation. Nos calculs de sections efficaces partielles intégrées et différentielles nous ont permis d'identifier ce type d'états dans la région allant jusqu'au cinquième d'ionisation simple. Certains ont été observés pour la première fois.

Title: Solvent effects on ion pairing and photoionization in water Author: Mgr. et Ing. Eva Pluhařová Department: Physical and Macromoleculer Chemistry Advisor: Prof. Pavel Jungwirth, DSc., IOCB AS CR, v.v.i. Advisor's e-mail address: pavel.jungwirth@uochb.cas.cz Abstract: Various methods of theoretical chemistry, namely classical molecular dynamics simulations with empirical force fields, ab initio molecular dynamics, enhanced sampling methods, and ab initio calculations were used to provide new insight into ion pairing and photoionization in aqueous solutions. Systems mod- eling aqueous solutions of decreasing size were investigated by computational methods of increasing level of sophistication. In a classical molecular dynamics study of concentrated lithium salt solutions, the electronic continuum correction to account for polarization provided qualita- tive improvement over the conventional non-polarizable force fields and enabled molecular interpretation of neutron scattering measurements. The same model- ing approach was also successful in predicting the affinity of halide ions to the solution/oil interface. By combining ab initio molecular dynamics and potential of mean force cal- culations, we designed a reliable computational protocol for calculating the free energy profile for an ion pair...

Dans cette thèse nous implémentons une approche Sturmienne, qui se sert de fonctions Sturmiennes généralisées (GSFs, en anglais), pour étudier l'ionisation de molécules par collisions de photons ou d'électrons. Comme l'Hamiltonian de la cible est non central, la description de l'ionisation des molécules n'est pas simple. En plus, puisque l'orientation spatiale de la molécule n'est généralement pas déterminée lors des expériences, une question importante à considérer est l'orientation aléatoire de la cible. Dans la littérature, des nombreuses méthodes théoriques ont été proposées pour traiter les molécules ; néanmoins, la plupart sont adaptées pour étudier, principalement, des états liés. Une description précise des états non-liés (continuum) des molécules reste un défi. Ici, nous proposons d'attaquer le problème avec les GSFs qui ont, par construction, un comportement asymptotique approprié au système étudié. Cette propriété permet de faire des calculs d'ionisation de façon plus efficace. Dans une première partie, nous validons l'implémentation de notre approche Sturmienne par l'étude de la photo-ionisation (PI) d'atomes. Différents potentiels effectifs sont utilisés pour décrire l'interaction de l'électron éjecté avec la cible ionisée. Les sections efficaces de PI sont calculées dans les jauges de longueur et de vitesse. Pour l'atome d'hydrogène la comparaison avec la formule analytique, indique qu'une convergence très rapide est obtenue avec un nombre modéré de GSFs. Pour He et Ne, nos résultats montrent, également, un très bon accord avec d'autres résultats théoriques et expérimentaux. Dans le cas des molécules, nous avons abordé l'orientation aléatoire avec deux stratégies : une utilise un potentiel moléculaire modèle (non-central), et l'autre un potentiel moyenné (central). Nous étudions la PI de CH4, NH3 et H2O à partir des orbitales de valence extérieure et intérieure, et aussi de SiH4 et H2S à partir des orbitales extérieures. Les sections efficaces de PI et les paramètres d'asymétrie (obtenus à partir des distributions angulaires) sont comparés avec ceux publiés dans la littérature. Nos résultats sont globalement satisfaisants et reproduisent les caractéristiques principales de ce processus d'ionisation. Dans une deuxième partie de la thèse, nous utilisons l'approche Sturmienne pour étudier l'ionisation de molécules par impact d'électrons. Pour le processus (e,2e), les sections efficaces triplement différentielles (TDCSs) sont examinées dans la première et deuxième approximation de Born, également en traitant de deux façons l'orientation aléatoire des molécules. Nous avons testé la méthode en comparent nos TDCSs pour l'atome d'hydrogène, montrant aussi son efficacité. Enfin, nous l'avons apliqué à l'ionisation de CH4, H2O et NH3, et nous avons comparé les résultats avec des données expérimentales et théoriques disponibles dans la littérature. Dans la plupart des cas, nos TDCSs sont en accord satisfaisant avec ces données, en particulier pour H2O et pour des électrons lents dans le cas de CH4 / In this PhD thesis we implement a Sturmian approach, based on generalized Sturmian functions (GSFs), to study the ionization of molecules by collision with photons or electrons. Since the target Hamiltonian is highly non-central, describing molecular ionization is far from easy. Besides, as the spatial orientation of the molecule in most experimental measurements is not resolved, an important issue to take into account is its random orientation. In the literature, many theoretical methods have been proposed to deal with molecules, but many of them are adapted to study mainly bound states. An accurate description of the unbound (continuum) states of molecules remains a challenge. Here we propose to tackle these problems using GSFs, which are characterized to have, by construction, the correct asymptotic behavior of the studied system. This property allows one to perform ionization calculations more efficiently. We start and validate our Sturmian approach implementation by studying photoionization (PI) of H, He and Ne atoms. Different model potentials were used in order to describe the interaction of the ejected electron with the parental ion. We calculated the corresponding PI cross sections in both length and velocity gauges. For H atom, the comparison with the analytical formula shows that a rapid convergence can be achieved using a moderate number of GSFs. For He and Ne we have also an excellent agreement with other theoretical calculations and with experimental data. For molecular targets, we considered two different strategies to deal with their random orientation: one makes use of a molecular model potential (non-central), while the other uses an angular averaged version of the same potential (central). We study PI for CH4, NH3, and H2O, from the outer and inner valence orbitals, and for SiH4 and H2S from the outer orbitals. The calculated PI cross sections and also the asymmetry parameters (obtained from the corresponding angular distributions) are compared with available theoretical and experimental data. For most cases, we observed an overall fairly good agreement with reference values, grasping the main features of the ionization process. In a second part of the thesis, we apply the Sturmian approach to study ionization of molecules by electron collisions. In the so-called (e,2e) processes, fully differential cross sections are investigated within both the first- or the second-Born approximations. Again, we show how to include in the description the random orientation of the molecule. We start with H atom, as a test system: the comparison of the calculated triple differential cross sections (TDCSs) with analytical results illustrates, similarly to the PI case, the efficiency of our GSF method. It is then applied to ionization of CH4, H2O and NH3, and comparisons are made with the few theoretical and experimental data available in the literature. For most cases, our TDCSs can reproduce such data, particularly for H2O and for slow ejected electrons in CH4

The research presented in this dissertation involves the development of chiral and achiral analysis using capillary electrochromatography (CEC) and CEC coupled to mass spectrometry (CEC-MS). Chapter 1 briefly reviews CEC fundamentals and latest development on chiral CEC and CEC-MS. The CEC-UV enantioseparations for several acidic compounds are described in Chapter 2. The optimum resolutions for these acidic enantiomers are achieved in ion-suppression mode, i.e. with an acidic mobile phase. One of major drawback in coupling CEC with MS is the bubble formation at the column outlet end, resulting in irreproducible retention time and erratic baseline, or even current breakdown. By introducing internal tapered columns, the aforementioned limitations of CEC-MS are successfully overcome in Chapter 3. The CEC-MS enantioseparation of warfarin and coumachlor is carefully investigated and applied to quantify R- and S-warfarin in human plasma. For individual enantiomers, a concentration of 25 ng/mL is detectable. To further improve the robustness of CEC-MS column, a new procedure of fabricating internal tapered columns is reported in Chapter 4. These internal tapered columns demonstrate excellent ruggedness, low background noise, and good compatibility in reversed-phase and polar organic modes of CEC-MS. In chapter 5, the feasibility of using internal tapered columns packed with vancomycin chiral stationary phase (CSP) is explored for simultaneous enantioseparation of eight â-blockers using CEC-MS. After a careful optimization of the mobile phase composition, sheath liquid and spray chamber parameter, 15 out of 16 enantiomers could be simultaneously resolved with excellent efficiency and detection sensitivity. The synthesis and characterization of sulfated and sulfonated cellulose phenylcarbamate CSPs is described in Chapter 6. The use of these CSPs, especially the sulfonated one, significantly enhances the EOF profile and sample throughput but maintain high enantiomeric resolving power under various modes of CEC and CEC-MS. By combining CEC and atmospheric pressure photo-ionization (APPI) MS, Chapter 7 demonstrates the separation and detection of mono-methylated benzo[a]pyrene (MBAP) isomers with ~100 times enhancement on detection sensitivity than CEC-UV. In Appedix 2, monolithic columns are synthesized through photopolymerized sol-gel approach and utilized for CEC and CEC-APPI-MS of polyaromatic hydrocarbons, and alkyl phenyl ketones.

No description available.

An enantioselective heart-cut two-dimensional liquid chromatography-atmospheric pressure photoionization-tandem mass spectrometry method was developed for the analysis of 25 methylsulfonyl polychlorinated biphenyl metabolites in tissue extracts. Enantioseparation was achieved for 9 out of the 10 chiral analytes in less than 91 minutes, improving upon previous gas chromatography-based methods. Use of a pyrenyl-ethyl silica column in the first dimension enabled separation of all but two pairs of isobaric analytes. Limits of detection of 0.01 to 1.73 ng on-column were achieved. The precision and accuracy were within acceptable limits, but poor sensitivity was achieved for several meta-methylsulfonyl-substituted congeners. Despite this limitation, the method was successfully applied to the analysis of Greenland sledge dog (Canis familiaris) plasma and adipose tissue extracts. Concentration and enantiomer fraction data are presented. None of the target analytes were detected in Norwegian glaucous gull (Larus hyperboreus) plasma extracts.

Orientador: Prof. Dr. Alexsandre Figueiredo Lago / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2015. / Neste trabalho original, sao apresentados os resultados inetidos de estudos sobre excitacao eletronica, fotoionizacao e dissociacao ionica em fase gasosa para a molecula de Tiazol (C3H3NS). Esta molecula se destaca por suas diversas aplicacoes em quimica, bioquimica, astrofisica e na industria. Observamos a escassez de informacoes relevantes para este sistema molecular na literatura, envolvendo estudos espectroscopicos e espectrometricos em fase gasosa. Assim, os resultados obtidos neste trabalho, sao considerados inetidos para este sistema molecular. Para realizacao de tais estudos, utilizou-se tecnicas de espectrometria de massas por tempo de voo (TOF-MS) em conjunto com as tecnicas espectroscopicas de coincidencia fotoeletron-fotoion(PEPICO), fotoeletron-fotoion-fotoion (PEPIPICO), producao total e parcial de ions. Para a ionizacao da amostra, empregou-se a Luz Sincrotron na regiao do ultravioleta de vacuo (UVV) e Raios-X. Os experimentos foram conduzidos nas linhas de Luz TGM, SGM e SXS do Laboratorio Nacional de Luz Sincrotron (LNLS) em Campinas, SP. Na faixa de energia de 9 a 21 eV, da interacao do fotons com com a amostra em fase gasosa e o progresso resultante da abertura de canais de fragmentacao ionica molecular. Foram propostas rotas reacionais de fotoionizacao e dissociacao ionica para a molecula e fragmentos, e determinacao dos rendimentos parciais ionicos (PIY). Com o aumento gradual da energia de interacao novas rotas de dissociacao se tornam energeticamente favoraveis, resultando no aparecimento de fragmentos com menor relacao massa/carga; isto, devido ao favorecimento na quebra das ligacoes quimicas, possibilitando rotas de dissociacao diversas. As principais rotas reacionais bem como principais fragmentos em destaque sao: C3H3NS + hv ¨ C3H3NS+ + e-; C3H3NS + hv ¨ C2H2S+ + HCN + e-; C3H3NS + hv ¨ CH2N + C2HS+ + e-. Os resultados deste trabalho para nivel de valencia, foram publicados na revista Journal of Mass Spectrometry. Os estudos relativo as camadas internas da molecula tambem foram realizados, em regioes com energias mais altas dos fotons, na regiao de Raio-X. Foram medidos espectros de rendimento total de ions (TIY) em energias cobrindo as bordas (camadas internas) dos elementos C 1s, N 1s, S 2p e S 1s; a partir dai foram propostas as transicoes eletronicas mais provaveis, originadas entre o estado fundamentcomo na regiao de UVV, rendimentos ionicos parciais (PIY) foram determinados nos estudos de camadas internas, utilizando a tecnica PEPIPICO, determinou-se qualitativamente os pares de ions mais importantes observados em coincidencias multiplas de reacoes de fotodissociacao em cada uma das bordas de absorcao estudadas. Para auxiliar nos resultados experimentais, e com o objetivo de obter parametros como estrutura eletronica, geometria dos estados fundamentais da molecula proposta e dos correspondentes cations obtidos por ionizacao e dissociacao, foram realizados calculos de quimica teorica usando metodos ab initio, utilizando o pacote de softwares GaussianR. / In this original project are presented novel results for the study of the electronic excitation, photoionization and ionic dissociation for the thiazole molecule in gas phase .This molecule stands out for its variety of different applications in chemistry, biochemistry, astrophysics and industries. We have noted a lack of relevant informations to this molecular system in the literature, involving spectroscopic and spectrometric studies in gas phase. Therefore, the results obtained from this work may be considered important new contributions to the field. In order to perform realize these studies, it we have used a was used mass spectrometry of time-of- flight (TOF-MS) together with the electron-ion coincidence techniques PEPICO, PEPIPICO, as well as total and partial ion yield techniques. As the ionizing source, the Synchrotron Light was used in the vacuum ultraviolet region (UVV) and X-ray ranges. The experiments were conducted at the on beam lines TGM, SGM and SXS in from the Brazilian Synchrotron Light Facility (LNLS), located in Campinas, SP. In the VUV range from 9 to 21 eV, it was observed the influence of the photon interaction on the gas phase sample and resulting progress on the opening of the molecular fragmentation channels. Reactional routes for the photoionization and ionic dissociation processes for the molecule and its fragments have been proposed, and the partial ion yields (PIY) determined. With the gradual increase of the photon energy, additional ion dissociation channels are energetically favorable, inducing chemical bonds rupture, and resulting in the appearence of fragments with lower mass/charge ratio. The photodissociation reaction observed from our spectra , as well as, the main ionic fragments in bold are: C3H3NS + hv ¨ C3H3NS+ + e-; C3H3NS + hv ¨ C2H2S+ + HCN + e-; C3H3NS + hv ¨ CH2N + C2HS+ + e-. from the valence studies for thiazole molecule have been recently published in the Journal of Mass Spectrometry. Inner shells studies have also been performed for this molecule at higher photon energies, in the soft and tender X-ray domains. We have recorded total ion yield spectra (TIY) covering the C 1s, N 1s, S 2p and S 1s edges, and based on the spectra we proposed the most likely electronic transitions related to the inner shells processes.The main electronic transitions found were: S 2p ¨ ¿�, we were able to determine and discuss, qualitatively, the most important pairs of ions generated in multiple coincidences from photodissociations reactions for each of the absorption edges studied. Ab initio calculations have been made in order to assist with the experimental data analysis and also aiming to obtain additional parameters such as: electronic structure, molecular neutral, ion, and fragments geometric structures, ionization energies, and so on. The theoretical studies were performed by using the GaussianR packages.

Made available in DSpace on 2016-12-12T20:15:49Z (GMT). No. of bitstreams: 1 Claudia Schmidt.pdf: 341536 bytes, checksum: e474da47db5271f6ff692ba3d3603ea9 (MD5) Previous issue date: 2012-07-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Rydberg atoms have as one of their characteristic the high principal quantum number. One consequence is the dimension of the order n2 implying in a large dipole moment, which allows one to use them for studies of atomic interactions with electromagnetic fields, including processes of photoionization. The increasing attention given to the investigation of photoionization cross sections of these highly excited atoms, is due to its importance to several areas like Atomic and Molecular Physics, Astrophysics, Plasma Physics, among others. Based on the model proposed by Aymar and co-workers, we studied the photoionization cross sections of some alkali atoms, namely, Sodium, Potassium, Rubidium and Cesium, expanding the previous analysis to n < 44. Since the photoionization processes can be enormously affected by the photoelectron energy, the we performed an analysis of the behaviour of radial wave functions depending on the photoelectron energies. And, this analysis, also studied the possible evidence of the Cooper minima. / Átomos de Rydberg têm como uma de suas principais características o alto numero quântico principal. Uma das conseqüências é a sua dimensão da ordem n2, implicando em um grande momento de dipolo, o que permite usá-los para estudos de interações atômicas com campos eletromagnéticos, incluindo processos de fotoionização. A atenção crescente dada a investigação de seções de choque de fotoionização desses átomos altamente excitados, é devido a sua importância para diversas áreas como Física Atômica e Molecular, Astrof&#305;sica, Física de Plasma, entre outros. Com base no modelo proposto por Aymar e colaboradores, estudamos as seções de choque de fotoionização de alguns átomos alcalinos, ou seja, Sódio, Potássio, Rubídio e Césio, ampliando a analise anterior para n < 44. Uma vez que os processos de fotoionização podem ser enormemente afetados pela energia dos fotoelétrons, realizou-se uma analise do comportamento das funções de onda radiais em função das energias do fotoelétron. E, desta analise, também estudamos a possível evidencia dos mínimos Cooper.

Photo-thermo-refractive (PTR) glass is an ideal photosensitive material for recording phase volume holograms. It is a homogeneous multi-component silicate glass that demonstrates all the advantages of optical glass: thermal stability, high laser damage threshold, and a wide transparency range. Moreover the ability to record phase patterns (i.e. spatial refractive index variations) into PTR glass has resulted in the fabrication of volume holograms with diffraction efficiency greater than 99%. The conventional method of recording a hologram in PTR glass relies on exposure to continuous-wave ultraviolet laser radiation. In this dissertation the interaction between infrared ultrashort laser pulses and PTR glass is studied. It is shown that photosensitivity in PTR glass can be extended from the UV region to longer wavelengths (near-infrared) by exposure to ultrashort laser pulses. It is found that there exists a focusing geometry and laser pulse intensity interval for which photoionization and refractive index change in PTR glass after thermal development occur without laser-induced optical damage. Photoionization of PTR glass by IR ultrashort laser pulses is explained in terms of strong electric field ionization. This phenomenon is used to fabricate phase optical elements in PTR glass. The interaction between ultrashort laser pulses and volume holograms in PTR glass is studied in two laser intensity regimes. At intensities below ~10^12 W/cm^2 properties such as diffraction efficiency, angular divergence, selectivity, and pulse front tilt are shown to agree with the theory of linear diffraction for broad spectral width lasers. A volume grating pair arrangement is shown to correct the laser pulse distortions arising from pulse front tilt and angular divergence. At higher intensities of irradiation, nonlinear generation and diffraction of third harmonic is observed for three types of interactions: sum-frequency generation, front-surface THG generation, and THG due to phase-matching with a grating formed by modulation of the nonlinear refractive index of PTR glass.

No description available.