Dissertations / Theses: 'Atom atom collision'

1

Glass, John T. "Relativistic ion-atom collision processes." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282153.

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2

Beyene, Musie. "Magnetic field control of ultracold atom-molecule collision." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3196/.

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In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.

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3

au, cplottke@fizzy murdoch edu, and Christopher Martin Plottke. "S-wave model in electron-atom collisions." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20040818.111937.

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This thesis discusses the theory and presents the numerical solution of the S-wave models of electron-hydrogen and electron-helium scattering. The Convergent Close-Coupling (CCC) method is used to obtain the numerical results. The focus within the electron-hydrogen S-wave model is to investigate cross section results for scattering from excited states; in particular, the elastic free-free transitions. These contain a divergent potential matrix element as the first term. The investigation of the electron-helium S-wave model is split into two sections, firstly applying the Frozen-Core approximation and then relaxing this approximation. This includes the first accurate ab initio calculation of double-excitation of helium.

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4

Quichaud, Viviane. "Etude des processus elementaires : de synthese de la molecule no, en post-decharge en ecoulement, de collisions titane-gaz rares, titane-molecules, par perturbation laser resolue en temps." Paris 6, 1987. http://www.theses.fr/1987PA066135.

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I. Etude de la preparation des etats excites de no dans un dispositif de post-decharge en ecoulement a partir de n::(2) excite (prepare par transfert d'excitation a partir d'atomes ar metastables dans une decharge basse pression) et de o (obtenu par dissociation de o::(2) dans une decharge de he). Observation d'une emission intense des bandes gamma de no, qui implique un etat a courte duree de vie (b) de n::(2) et le premier etat metastable de o. Ii. Analyse des processus d'extinction et de transfert d'excitation a partir d'etats a courte duree de vie de ti (crees dans un dispositif a cathode creuse) lors de collisions avec des gaz rares (ar, ne, he) et des molecules (n::(2),h::(2)). Ces experiences permettent l'etude de cinetiques de reactions elementaires au sein d'un plasma basse pression ensemence de vapeurs metalliques, a l'aide du dispositif de post-decharge en ecoulement

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5

Harland, Peter W. "Studies of gas phase electron, ion and atom collision processes." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/14990.

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The research papers submitted in this thesis describe experimental and theoretical investigations of particle collisions in which the projectiles have been electrons, ions and atoms, and the targets have been atoms and molecules. Non-reactive and reactive collisions have been studied in order to explore the fundamental nature of the collision event, to understand the dynamics, and to facilitate the determination of thermochemical parameters and reaction properties. The formation of positive and negative ions under single collision conditions as a function of electron impact energy has been investigated for small molecules and for molecular clusters. The measurement of accurate ionization efficiency curves and ionization thresholds has been achieved using custom designed near-monochromatic electron sources or analytical deconvolution. In many cases, detailed energy balancing has been attempted through the measurement of the recoil energies of fragment ions using retarding electric fields. Ionization mechanisms for associative and dissociative resonance electron capture and the formation of isomeric positive ions have been deduced. Thermochemical parameters, including electron affinities, ionization potentials, enthalpies of formation and bond dissociation energies, have been determined. Experiments in which the molecular targets were spatially oriented have shown, for the first time, that the mass spectrum and the ionization efficiency are orientation dependent. A theoretical model has been developed which accounts for the experimental measurements. Investigations of ion-molecule chemistry and non-reactive ion-molecule interactions have been carried out using a custom designed drift-tube mass spectrometer. It has been shown that isomeric ions can be distinguished by their ion transport properties and that the isomeric form of an ion-molecule reaction product ion can be directly measured. A theoretical model based on a generalised ion-helium interaction potential was developed which quantitatively accounted for the relative ion mobilities of a wide range of ions according to their physical properties.

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6

Astruc, Jean-Pierre. "Transfert d'électron entre atomes excités et molécules dans une expérience en jets croisés avec fluorescence résolue dans le temps." Paris 13, 1987. http://www.theses.fr/1987PA132020.

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Etude experimentale avec résolution temporelle à l'échelle de la nanoseconde des valeurs absolues des séctions efficaces pour les transferts partiels d'énergie électronique entre Na(4d) et He, Ar, N(2), O(2), N(2)o et SF(6). Développement quantitatif de deux modèles à intermediaire ionique : réseau de multicroisement et diffusion résonnants atome excité-molecule. Emploi de l'approximation d'impact avec correction d'effet de coeur pour la transfert de moment orbital na(4d -> 4f)

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Konishi, Hideki. "Collisional stability of localized metastable ytterbium atoms immersed in a Fermi sea of lithium." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225386.

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8

Dalibard, Jean. "Le rôle des fluctuations dans la dynamique d'un atome couple au champ électromagnétique." Paris 6, 1986. http://www.theses.fr/1986PA066393.

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Etude de la dynamique atomique interne; possibilité de séparer la contribution des fluctuations du vide et de la réaction du rayonnement pour differents processus radiatifs (émission spontanée, déplacement de Lamb, etc. ). Etude de la dynamique atomique externe en partant de l'analogie entre ce problème et celui du mouvement brownien; établissement d'une équation de Fokker-Planck-Kramers pour l'évolution de la fonction de Wigner atomique, avec termes de force stationnaire, force de frottement etc. Etude détaillée du mouvement atomique dans une onde laser stationnaire intense: refroidissement, piégeage.

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9

Gadea, Florent Xavier. "Theorie des hamiltoniens effectifs : applications aux problemes de diabatisation et de collision reactive." Toulouse 3, 1987. http://www.theses.fr/1987TOU30276.

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Etude approfondie sur la theorie des hamiltoniens effectifs et analyse de leurs applications aux methodes de diabatisation et au traitement des collisions reactives. Propositions pour le calcul des valeurs propres de l'hamiltonien par des methodes de perturbation ou iteratives, pour l'emploi d'hamiltoniens effectifs dans le calcul des surfaces quasi diabatiques et le traitement general des collisions reactives. Application a la reaction cs+h::(2) etudiee par les methodes ab initio pour la geometrie colineaire : surfaces de potentiel, sections efficaces et mecanismes predominants

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10

Lühr, Armin. "Collisions of low-energy antiprotons and protons with atoms and molecules." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16084.

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In dieser Arbeit wird eine, zeitabhängige, nicht störungstheoretische numerische Methode entwickelt, welche Ionisation und Anregung von Atomen oder Molekülen in Stößen mit entweder PB oder P beschreibt und auf der impact-parameter Methode basiert. Es wird eine spektrale close-coupling Methode verwendet, um die zeitabhängige Schrödinger-Gleichung zu lösen, in welcher die Wellenfunktion in (effektive) Ein- oder Zwei-Elektronen-Eigenzustände des Targets entwickelt wird. Dies beinhaltet auch eine erstmalige volle Zwei-Elektronen-Beschreibung von H2 in PB-Stößen. Rechnungen werden für PB-Stöße mit H, H2+ und H2 sowie He und den Alkaliatomen Li, Na, K und Rb durchgeführt. Daten für P-Stöße werden für H2 und die Alkaliatomen Li, Na und K erzielt. Die Methode wird durch einen detaillierten Vergleich der erhaltenen Ergebnisse für P-Stöße und für PB + He mit Literaturdaten verifiziert. Andererseits ergänzen die totalen und differentiellen Wirkungsquerschnitte für Ionisation und Anregung der Targets in PB-Stößen die spärliche Literatur. Sowohl die Resultate für verschiedene Targets als auch für PB- und P-Stöße werden miteinander verglichen. Ein Schwerpunkt dieser Arbeit liegt auf der Untersuchung von PB + H2, welche die Abhängigkeit der Wirkungsquerschnitte vom Kernabstand und von der relativen Ausrichtung der molekularen Achse beinhaltet. Weiterhin werden Ergebnisse mit Ein-Elektronen-Modellpotentialen erzielt und mit der vollen Zwei-Elektronen-Beschreibung von H2 verglichen. Außerdem werden Energieverluste in PB-Stößen bestimmt.
In this work a nonperturbative, time-dependent numerical approach is developed which describes ionization and excitation of atoms or molecules by either PB or P impact based on the impact-parameter method. A spectral close-coupling method is employed for solving the time-dependent Schrödinger equation in which the scattering wave function is expanded in (effective) one- or two-electron eigenstates of the target. This includes for the first time a full two-electron, two-center description of the H2 molecule in PB collisions. The radial part of the one-electron eigenstates is expanded in B splines while the two-electron basis is obtained with a configuration-interaction approach. Calculations are performed for PB collisions with H, H2+, and H2 as well as with He and alkali-metal atoms Li, Na, K, and Rb. Additionally, data are obtained for P collisions with H2, Li, Na, and K. The developed method is tested and validated by detailed comparison of the present findings for P impacts and for PB + He collisions with literature data. On the other hand, total and differential cross sections for ionization and excitation of the targets by PB impact complement the sparse literature data of this kind. Results gained from different targets as well as from PB and P impact are compared with each other and assessed. Furthermore, results obtained with one-electron model potentials are compared to the full two-electron description of H2. Finally, stopping powers for PB impacts are determined.

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11

Taoutioui, Abdelmalek. "Étude théorique de la dynamique électronique au cours de collisions entre des ions et des cibles atomiques hautement excitées." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS323.

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La compréhension des processus électroniques ayant lieu au cours de collisions atomiques présente un intérêt important pour la modélisation de phénomènes observés dans des systèmes complexes tels que les milieux atmosphériques, astrophysiques et biologiques. Ces processus se manifestent au niveau microscopique mais jouent un rôle déterminant sur l’évolution et les propriétés physico-chimiques de ces systèmes macroscopiques. D’un point de vue fondamental, les collisions sont également des "laboratoires" privilégiés pour l'étude de systèmes quantiques à N-corps. Les collisions ion-atome sont d'une importance cruciale dans plusieurs domaines tels que celui concernant la fusion nucléaire par confinement magnétique : la compréhension des processus électroniques est nécessaire pour la modélisation de ce type de plasmas. Cette thèse se situe dans ce contexte et est dédiée à l’étude théorique des processus électroniques qui se manifestent au cours de collisions entre des ions et des cibles atomiques hautement excitées. Dans ce travail, nous avons privilégié la modélisation de la capture électronique et le calcul des sections efficaces pour le système proton-hydrogène. Nous avons adopté deux approches théoriques non perturbatives : la méthode classique CTMC et une méthode semi-classique SCAOCC. Nous avons calculé les sections efficaces totales et partielles de capture pour des cibles excitée initialement jusqu’à la couche n=7. Des comparaisons entre les résultats issus de ces méthodes et les quelques données théoriques disponibles sont réalisées et représentent l’originalité du travail. Des lois d’échelle empiriques pour les sections efficaces totales sont également décrites
The understanding of the electronic processes taking place during atomic collisions is of great interest for the modeling of phenomena observed in complex systems such as atmospheric, astrophysical and biological environments. These processes manifest at the microscopic level but play a determining role on the evolution and the physicochemical properties of these macroscopic systems. From a fundamental point of view, collisions are also privileged "laboratories" for the study of quantum systems with N-bodies. Ion-atom collisions are of crucial importance in several fields such as that concerning nuclear fusion by magnetic confinement: the understanding of the electronic processes is necessary for the modeling of this type of plasmas. This thesis is situated in this context and is dedicated to the theoretical study of the electronic processes that occur during collisions between ions and highly excited atomic targets. In this work, we privileged the modeling of the electronic capture and the computation of the cross sections for the proton-hydrogen system. We adopted two non-perturbative theoretical approaches: the classical CTMC method and a semi-classical SCAOCC method. We calculated the total and partial capture cross sections for targets initially excited up to the n = 7 layer. Comparisons between the results of these methods and the few theoretical data available are made and represent the originality of the work. Empirical scale laws for total cross sections are also described

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12

Haffad, Abdelkrim. "Angular momentum transfer in electron-atom and atom-atom collisional ionization." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/29826.

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13

Spratt, David James. "Electron loss and excitation in atom-atom collisions." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287429.

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14

Girard, Bertrand. "Etude de la collision reactive ii + f -> if + i par fluorescence induite par laser." Paris 6, 1987. http://www.theses.fr/1987PA066398.

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Etude de cette collision par la methode des faisceaux croises et grace a la transition (b <- x) intense, dans le visible, apres analyse de la saturation du processus d'excitation laser de cette transition de if forme. Deduction des populations des differents niveaux rovibrationnels de l'etat x. Etablissement d'une cartographie detaillee de la distribution rotationnelle des niveaux vibrationnels v = 8 a 20 de l'etat x de if: aspect bimodal qui implique la coexistence de deux chemins reactionnels differents. Attribution a un artefact de l'important signal observe anterieurement pour v = 0. Mesures preliminaires de la section efficace differentielle par effet doppler

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15

Thomsen, Laura Kathrine Wehde, and n/a. "Using Quantum Feedback to Control Nonclassical Correlations in Light and Atoms." Griffith University. School of Science, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040406.124012.

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This thesis considers two types of applications of quantum feedback control; feedback creation of nonclassical states of light, and controlling nonclassical properties of an ensemble of atoms. An electro-optical feedback loop will create an in-loop field with nonclassical photon statistics similar to squeezed light, resulting in fluorescence line-narrowing of a two-level atom coupled to such light. We extend this theory to study a three-level atom coupled to broadband squashed light, and confirm the two-level atom line-narrowing using a more realistic non-Markovian description of the feedback loop. The second type of application utilizes continuous QND measurement of atomic ensembles. If we measure the collective spin, then the system experiences conditional spin squeezing dependent on the measurement results. We show that feedback based on these results can continuously drive the system into the same conditioned state, resulting in deterministically reproducible spin squeezing. If we measure the atom number fluctuations of a BEC, then, due to the nonlinearity of atomic self interactions, this is also information about phase fluctuations. We show that feedback based on this information can greatly reduce the collisional broadening of the linewidth of an atom laser out-coupled from the condensate.

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16

Horton, Timothy Scott. "COLLISIONAL AND RADIATIVE RELAXATION IN SODIUM DIMER AND ARGON ATOM COLLISIONS." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1480693544113525.

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17

Radouani, Abdelhak. "Réaction des atomes métastables de gaz rares (Ar*(3p2,0), Kr*(3p2) et Xe*(3p2)) avec le silane." Grenoble 1, 1986. http://www.theses.fr/1986GRE10143.

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Etude des produits de reactions par spectrometrie d'emission et de si a l'etat fondamental pas spectrometrie d'absorption. Absence d'emission dans le cas de xe et observation de la formation de si dans differents etats electroniques excites et de sih dans son 1er etat electronique excite, pour lesquels on determine les coefficients de chimiluminescence. Avantages de la technique de post-decharge en ecoulement. Emploi d'un modele statistique pour interpreter l'evolution des populations des niveaux rotationnels de sih**(*) par collision avec ar

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18

BERGNES, BRASEY CHANTAL. "Etude des processus directs elastique et inelastiques se produisant lors de la collision entre un ion d'helium et une cible d'hydrogene, pour une energie variant de 1,5 a 30 kev." Toulouse 3, 1988. http://www.theses.fr/1988TOU30204.

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Etude des sections efficaces doublement differentielles des processus elastiques et inelastiques au cours de la collision d'un faisceau d'ions de he avec h ou h::(2), entre 1,5 et 30 kev, pour des angles de diffusion compris entre 5' et 30**(o), par spectrometrie de perte d'energie du projectile. Comparaison des resultats a des valeurs calculees et mesurees anterieurement a d'autres auteurs. Proposition d'un modele permettant d'interpreter les resultats pour la cible h

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19

O'Rouke, Sheelagh Francesca Camille. "Theory of ion-atom collisions." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334486.

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20

McSherry, D. M. "Ionization in ion-atom collisions." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368567.

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21

LaForge, Aaron Christopher. "Three-body dynamics in single ionization of atomic hydrogen by 75 keV proton impact." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2010. http://scholarsmine.mst.edu/thesis/pdf/Laforge_09007dcc80798b26.pdf.

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Thesis (Ph. D.)--Missouri University of Science and Technology, 2010.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 21, 2010) Includes bibliographical references (p. 82-87).

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22

Rossi, François-Noël. "Etude théorique des collisions non réactives entre atomes alcalins et molécules d'hydrogène ou de deuterium : Calcul et analyse des surfaces de potentiel, application aux transitions de structure fine du rubidium." Paris 13, 1986. http://www.theses.fr/1986PA132015.

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Calcul des courbes de potentiel adiabatiques pour les géométries colinéaires et perpendiculaires, à l'aide d'un pseudopotentiel dépendant du moment orbital électronique et d'une approche à deux centres; bon accord avec les calculs ab initio existants. Examen des différentes symétries de ces systèmes dans le formalisme de la théorie des groupes, afin d'étudier les valeurs propres et facteurs propres de l'hamiltonien électronique. Calcul quantique des sections efficaces relatives des transitions de structure fine de Rb induites par collision avec H(2) ou D(2). En tenant compte des niveaux rotationnels moléculaires, obtention d'un très bon accord avec les résultats expérimentaux et interprétation de l'effet isotopique

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23

Muniz, Sérgio Ricardo. "Estudo de Blindagem Óptica em Colisões Frias." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-06052005-162937/.

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Neste trabalho, mostramos que é possível suprimir a maioria dos processos inelásticos que podem causar perdas de átomos em armadilhas magneto-ópticas. Nossos resultados revelam que o processo de blindagem óptica (demonstrado pelo nosso grupo, pela primeira vez para o processo de ionização fotoassociativa Phys. Rev. Lett. 73, 1911 (1994)) é bem mais geral do que se supunha. Permitindo, inclusive, a supressão de colisões entre átomos no estado fundamental. E provavelmente qualquer outro processo inelástico que ocorra a curtas distâncias internucleares. Para se chegar a esses resultados, foi necessário desenvolver uma nova técnica de aprisionamento, que permite o estudo de colisões frias, mesmo em armadilhas cujo potencial de confinamento é pequeno. Graças a essa técnica foi possível, pela primeira vez, observar perdas causadas por mudança de estrutura hiperfina, numa armadilha de átomos de sódio operando na linha D1 (carregada a partir de uma célula de vapor). Essa técnica ainda nos permitiu medir a taxa de colisões frias () no trap da linha D1, um dado que até então não existia na literatura. Para verificar a confiabilidade dos resultados obtidos por essa técnica, realizamos também medidas de  na linha D2 e comparamos esses resultados com outros existentes na literatura (obtidos por uma técnica diferente). A boa concordância entre esses resultados nos deixa confiantes em dizer que essa técnica, além de ser muito interessante, no estudo de armadilhas rasas (seja isso devido à intensidade dos lasers de aprisionamento, seja devido a natureza própria da armadilha), é também bastante confiável
In this work, we showed that is possible to suppress most of the inelastic processes that may cause losses of atoms in a magneto-optical trap. Our results reveal that the process of optical shielding (demonstrated by our group, for the first time to photoassociative ionization - Phys. Rev. Lett. 73, 1911 (1994)) is much more general than it was supposed. Even allowing the suppression of ground state collisions and probably any other inelastic process that happens at short internuclear distances. To achieve those results, it was necessary to develop a new trapping technique, which allows the study of cold collisions, even in traps whose confinement potential is small. Thanks to that technique it was possible, for the first time, to observe losses caused by hyperfine changing collisions, in a trap of sodium atoms operating in the D1 line (loaded from a vapor cell). That technique has still allowed us to measure the rate of cold collisions () for the D1 line trap, a result which, until now, did not exist in the literature. To verify the reliability of the results obtained by that technique, we also accomplished measures of  in the D2 line and compared those results with other existent ones in the literature (obtained by a different technique). The good agreement among those results, made us confident in saying that this technique, besides being very interesting in the study of shallow traps (due to the intensity of the trapping lasers, or due to the own nature of the trap), it is also quite reliable.

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24

Boutalib, Abderrahim. "Etude théorique de la surface de potentiel du système HO::(2) + H. : Influence de la corrélation électronique." Pau, 1986. http://www.theses.fr/1986PAUU3009.

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Calcul des géométries du points de sille et des barrières d'activation pour les réactions d'abstraction (HO::(2) + H->H::(2) + O::(2)) et d'approche concertée (HO::(2) + H->H::(2)O + O) pour la méthode SDCI à l'ordre d'une base DZ dans la région de valence, augmentée par des orbitales de polarisation de type D sur chaque atome O. Evaluation des paramètres cinétiques dans le cadre de la théorie de l'état de transition : énergies d'activation et constantes de vitesse. Faible probabilité du mécanisme de réaction concertée

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25

Davies, Hilary Jane. "An optically guided atomic fountain." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4580/.

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This thesis describes the development of a laser-cooling experiment aimed at efficient transfer of cold atoms over a short distance, for loading into a conservative atom trap. We detail the construction of a 3D magneto-optical trap (MOT) and perform characterisation measurements to optimise the number and temperature of the cold atoms. The atoms are launched vertically in a fountain from the MOT using a 'moving molasses' technique and a red-detuned far-off-resonant laser beam is used to guide them into an UHV chamber. Loading into the guiding beam is optimised with respect to the beam and MOT parameters. We demonstrate a maximum loading of 20% and guiding over a distance of more than 10 cm without loss of atoms. The atoms are delivered to the UHV chamber in a cloud with a transverse dimension of order 200 µm. We discuss the extension to continuous operation of the guided atomic fountain. The 3D MOT is replaced by a funnel with 2D trapping and 3D cooling which continuously extracts the cold atoms using moving molasses. A comparison between the flux of guided atoms obtained in a pulsed fashion from the 3D MOT and continuously from the funnel indicate that the pulsed case is a factor of ten more efficient. The difference is due to inferior loading from the funnel. The optically guided fountain is used to load an optical dipole trap in the UHV chamber, using an 'optical trap door'. No additional cooling is required. The dynamics of the atoms in the optical dipole trap are studied. We discuss multiple loading of a conservative trap with the view of accumulating more atoms than can be obtained in a MOT.

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26

Bradley, J. P. "Charge transfer during ion-atom collisions." Thesis, Queen's University Belfast, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426960.

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27

Truhins, Kaspars. "Stereodynamics of asymmetric rotor - atom collisions." Thesis, University of Sussex, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363381.

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BARDET, JEAN-PAUL. "Contribution a l'etude de l'effet d'anode dans les electrolytes fondus tel le melange equimoleculaire licl-kcl fondu." Paris 6, 1986. http://www.theses.fr/1986PA066585.

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Le calcul des profils theoriques de la raie semi-degeneree li (i) 4f4d4p->2p, incluant une correction tenant compte de l'effet dynamique des ions permet de preciser les principaux parametres du plasma duodique obtenu par electrolyse du melange equimoleculaire fondu licl-kcl. Methode de calcul systematique des elements matriciels de l'operateur omega (t) intervenant dans le formalisme de magnus, pour tout alcalin, pour des collisions electroniques faibles et fortes. Les resultats donnes, appliques aux niveaux n = 4, permettent de confirmer les valeurs numeriques des parametres du plasma (t::(e),n::(e)) et de verifier que les conditions de la limite d'impact sont atteintes

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29

Bensitel, Abdeslam. "Spectroscopie des ions de recul d'argon produits par impact d'ions lourds dans le domaine 90-850a." Caen, 1988. http://www.theses.fr/1988CAEN2003.

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Identification de 417 raies de ar i a ar ix et de nouvelles raies de ar vi a ar vii dans le domaine 90-850 a obtenues par impact d'ions lourds d'energie inferieur au mev/nucleon. Obtention de differents types de spectres suivant le fonctionnement du faisceau: 1) en continu, spectre total a 2 dimensions (intensite, longueur d'onde) correspondant a l'emission prompte, 2) en pulse, spectre a 3 dimensions (intensite, temps, longueur d'onde) associe a l'emission retardee. Mise en evidence de phenomenes de capture electronique par collisions secondaires entre ions de recul et ar neutre, conformement aux previsions du modele classique de la barriere de potentiel

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30

Elayoubi, Mustapha. "Transfert d'atomes d'hydrogène vers la cathode d'un arc réducteur de composition argon-hydrogène /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1989. http://theses.uqac.ca.

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31

Patel, Akshay. "Intense laser atom interactions." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341059.

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32

Mercier-Depuydt, Eliane. "Contribution a l'etude des collisions ion-atome a basse energie : un modele semi-diabatique pour les courbes de potentiel des ions moleculaires arh**(+*) et hene**(+*)." Paris 6, 1987. http://www.theses.fr/1987PA066522.

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Proposition d'un modele semi-adiabatique pour les ions dissymetriques excitess, formes d'un "coeur" adiabatique et d'un electron externe (de type h::(2)**(+)) en vue de calculs ab initio precis et de la determination des courbes de potentiel necessaires a l'interpretation des collisions a basse energie. Applicaion a arh**(+*): calcul des courbes de potentiel quasidiabatiques pour r = 1,7 - 7 ua; etude du seuil de la reaction ar**(+) + h -> ar**(+) + h (n=2). Application a hene**(+*). Interpretation des oscillations de rosenthal observees dans la section efficace totale d'excitation; calcul des courbes de potentiel ab initio adiabatiques du coeur hene**(2+), des coefficients d'einstein entre les etats moleculaires de ce coeur et des etats quasi diabatiques de coeur par extension de la methode de l'hamiltonien effectif de b. Levy

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33

Plottke, Christopher Martin. "S-wave model in electron-atom collisions." Plottke, Christopher Martin (2004) S-wave model in electron-atom collisions. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/262/.

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This thesis discusses the theory and presents the numerical solution of the S-wave models of electron-hydrogen and electron-helium scattering. The Convergent Close-Coupling (CCC) method is used to obtain the numerical results. The focus within the electron-hydrogen S-wave model is to investigate cross section results for scattering from excited states; in particular, the elastic free-free transitions. These contain a divergent potential matrix element as the first term. The investigation of the electron-helium S-wave model is split into two sections, firstly applying the Frozen-Core approximation and then relaxing this approximation. This includes the first accurate ab initio calculation of double-excitation of helium.

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34

McCartney, Mark. "Ionization processes in multielectron ion-atom collisions." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359106.

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35

Zamkov, Mikhail. "Multi-electron processes in Ion-atom collisions /." Search for this dissertation online, 2003. http://wwwlib.umi.com/cr/ksu/main.

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36

Götz, Simone Andrea [Verfasser], and Matthias [Akademischer Betreuer] Weidemüller. "A high density target of ultracold atoms and momentum resolved measurements of ion-atom collisions / Simone Andrea Götz ; Betreuer: Matthias Weidemüller." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1179784596/34.

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37

Støchkel, Kristian. "Electron-transfer processes in fast ion-atom collisions." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-732.

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38

Forster, Christine. "Aspects of charge exchange in ion-atom collisions." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6189/.

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The straight line semi-classical Impact Parameter method has been modified for use with classical trajectories. Ion-atom collisions have been modelled using wavefunctions expanded in terms of atomic basis states which were centred on either the target or projectile ions. Total and differential charge exchange cross-sections are presented for (^4)He(^++) and (^4)He(^+) collisions within the centre of mass energy range 0.21 kev < E(_em) < 2.5 keV. Results using curved and straight line paths are compared with data from other authors. Significant trajectory effects were found at the lower energies in the range. The curved trajectory results were lower than those from the straight line model and also lower than previous calculations carried out. At higher energies in the range there was good agreement between straight line and curved trajectory models and previous work. Differential cross-sections were found to be sensitive to the trajectories employed, and comparisons have been made with previous work. Total, state specific and differential cross- sections for charge exchange are presented for Be(^++) and H collisions using a five state basis, within the centre of mass energy range 0.111 keV < E(_em) < 0.4444 keV. There was reasonable agreement between the straight line results and previous work. There were significant trajectory effects for all the final charge transfer states. Results are presented for low-energy collisions between positively charged muons and atomic hydrogen. An eight state basis has been used. Direct excitation cross sections for n = 2 atomic states and charge transfer cross sections to Is and n = 2 have been calculated. The effect on the cross sections of using different internuclear potentials has been examined. Trajectory effects were small for charge transfer to Is but were more pronounced in the direct excitation and charge exchange cross- sections to n = 2. These results have been compared to those obtained for curved trajectory H(^+) and H collisions at the same relative velocity, to assess the validity of velocity scaling. It was found that velocity scaling was reliable for charge transfer to Is and for total electron capture cross-sections. However, it was progressively inaccurate for direct excitation and for electron capture into excited states for µ(^+) impact energies of less than 300 eV. These results are discussed and suggestions for further work are made.

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39

Dunseath, Kevin Murray. "Transfer and ionisation processes in ion-atom collisions." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335336.

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40

Nagy, O. Z. I. "Analysis of electron-atom and electron-molecule collisions." Thesis, University of Stirling, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370537.

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41

Campbell, Eleanor Elizabeth Bryce. "Electronic and vibrational excitation in atom/molecule collisions." Thesis, University of Edinburgh, 1986. http://hdl.handle.net/1842/13295.

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42

Lu, Jun. "Classical trajectory Monte Carlo simulation of ion-Rydberg atom collisions." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968439713.

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43

Lemoine, Didier. "Étude quantique des transferts inélastiques dans les collisions atome-atome et atome-molécule." Lille 1, 1988. http://www.theses.fr/1988LIL10014.

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1°. Étude des transferts entre composantes de structure fine d'un atome alcalin dans un état électronique doublet p induits par collision avec un atome sans structure ; détermination des sections efficaces et description totalement adiabatique de la dynamique de collision, mettant en évidence un nouveau mécanisme de couplage. 2°. Étude des transferts rotationnels dans N(2) (état fondamental) et Li(2) (premier état excité) induits par collision avec un atome de gaz rare ; exploration du domaine de validité des deux approximations couramment utilisées ; étude de la distribution angulaire de la diffusion dans le système du centre de masse pour N(2)-Ne ; explication de l'origine des effets d'asymétrie observés dans les transitions rotationnelles pour Li(2)-He, Ne.

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44

Patton, Conrad John. "Coincidence studies of ionizing and charge changing collisions." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318819.

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45

Abbas, Isam Ahmed. "Studies of the dynamics of ion molecule collisions using cross beam technique." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/10787.

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46

Hewitt, Robin Nicholas. "An L² representation of the continuum in heavy particle collisions." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6770/.

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This thesis is concerned with the use of L² or square integrable functions as a representation of the electronic continua in ion-atom collisions. An exact representation of the continuum states is considered for comparison. The functions are optimised in an attempt to remove some of the arbitrary features present in such calculations. The original work of this thesis is mainly concerned with the calculation of single electron processes in collisions between He²⁺ ions and neutral lithium atoms. The cross sections for single electron capture were calculated in a close-coupled approximation, using the semi-classical impact parameter method. A maximum of thirty-two atomic orbitals with plane-wave translational factors attached were centred upon the target and projectile. Satisfactory agreement with experimental data is obtained over the He(^2+)laboratory energy range from 8 to 2000 keV. The results show the importance of the continuum over a restricted range of impact energies. The rest of the research is concerned with direct excitation and ionisation in the same collision system and results are given for He²⁺ laboratory energies between 20 and 6000 keV. The calculations used a similar close-coupled approximation with up to sixty-five basis states. The best ionisation cross sections reproduce the experimental data apart from a normalization factor. The excitation results were more sensitive to basis set choice. The ionisation cross sections were also investigated using an exact representation of the continuum states, using the First Born Approximation and a t-matrix approximation in an attempt to improve upon the L² results. The relationship between the present calculations and some previous methods are discussed and suggestions for future work are made. These are the first close-coupled estimates of ionisation for this sytem and show that contributions from target d- and f- states dominate the ionisation cross section around its maximum.

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47

Atan, H. "Charge changing experiments and multipole expansions of electron loss to the continuum." Thesis, University of Sussex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257742.

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48

Osborne, Mark Allen. "Rotational transfer in diatomic and polyatomic molecules." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239696.

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49

Bull, James. "Application of Quantum Mechanics to Fundamental Interactions in Chemical Physics: Studies of Atom-Molecule and Ion-Molecule Interactions Under Single-Collision Conditions: Crossed Molecular Beams; Single-Crystal Mössbauer Spectroscopy: Microscopic Tensor Properties of ⁵⁷Fe Sites in Inorganic Ferrous High-Spin Compounds." Thesis, University of Canterbury. Department of Chemistry, 2010. http://hdl.handle.net/10092/4292.

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As part of this project and in preparation for future experimental studies of gas-phase ion-molecule reactions, extensive modification and characterization of the crossed molecular beam machine in the Department of Chemistry, University of Canterbury has been carried out. This instrument has been configured and some preliminary testing completed to enable the future study of gas-phase ion-molecule collisions of H⁺₃ and Y⁻ (Y = F, Cl, Br) with dipole-oriented CZ₃X (Z = H, F and X = F, Cl, Br). Theoretical calculations (ab initio and density functional theory) are reported on previously experimentally characterized Na + CH₃NO₂, Na + CH₃NC, and K + CH₃NC systems, and several other systems of relevance. All gas-phase experimental and theoretical studies have the common theme of studying collision orientation dependence of reaction under singlecollision conditions. Experimental measurements, theoretical simulations and calculations are also reported on some selected ferrous (Fe²⁺) high-spin (S=2) crystals, in an attempt to resolve microscopic contributions of two fundamental macroscopic tensor properties: the electric-field gradient (efg); and the mean square displacement (msd) in the case when more than one symmetry related site of low local point-group symmetry contributes to the same quadrupole doublet. These determinations have been made using the nuclear spectroscopic technique of Mössbauer spectroscopy, and complemented with X-ray crystallographic measurements.

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50

Green, P. S. "Theory of double charge transfer in ion-atom collisions." Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637093.

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A theory of double-charge-transfer processes in ion-atom collisions has been developed. The collision energies of interest, in the range 3-10 keV permit the use of semi-classical impact parameter formalism within which Landau-Zener theory has been adapted to describe the coupling that arises indirectly from 2 virtual 1-electron transitions, necessary because the direct 2-electron coupling amplitudes are insignificant in comparison. A consistent treatment of adiabatic and diabatic potential energy curves and techniques needed to locate crossings of the latter type are given. Application to scattering of OH⁺ and F⁺ by inert gas atoms require a systematic treatment of non spherical p atomic orbitals in the theory. Explicit rotations from space-fixed to body-fixed co-ordinates at each point in the scattering trajectory revealed that the theory can predict effects, which in theories involving only s orbitals require a rotational coupling operator, in the absence of such coupling. Cross sections for various double-charge-transfer scattering processes are calculated, employing established model 1-electron transfer scattering amplitudes and reproduced well the experimentally observed "reaction windows" of projectile energy loss within which the cross sections are significant. General kinematic factors, rather than the inclusion of a systematic treatment of the non-spherical p orbitals involved in the reactions studied, are primarily responsible for the form of the reaction window.

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Dissertations / Theses on the topic 'Atom atom collision'

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