Resonant states are multiply excited states in atoms and ions that have enough energy to decay by emitting an electron. The ability to emit an electron and the strong electron correlation (which is extra strong in negative ions) makes these states both interesting and challenging from a theoretical point of view. The main contribution in this thesis is a method, which combines the use of B splines and complex rotation, to solve the three-electron Schrödinger equation treating all three electrons equally. It is used to calculate doubly excited and triply excited states of 4S symmetry with even parity in He-. For the doubly excited states there are experimental and theoretical data to compare with. For the triply excited states there is only theoretical data available and only for one of the resonances. The agreement is in general good. For the triply excited state there is a significant and interesting difference in the width between our calculation and another method. A cause for this deviation is suggested. The method is also used to find a resonant state of 4S symmetry with odd parity in H2-. This state, in this extremely negative system, has been predicted by two earlier calculations but is highly controversial. Several other studies presented here focus on two-electron systems. In one, the effect of the splitting of the degenerate H(n=2) thresholds in H-, on the resonant states converging to this threshold, is studied. If a completely degenerate threshold is assumed an infinite series of states is expected to converge to the threshold. Here states of 1P symmetry and odd parity are examined, and it is found that the relativistic and radiative splitting of the threshold causes the series to end after only three resonant states. Since the independent particle model completely fails for doubly excited states, several schemes of alternative quantum numbers have been suggested. We investigate the so called DESB (Doubly Excited Symmetry Basis) quantum numbers in several calculations. For the doubly excited states of He- mentioned above we investigate one resonance and find that it cannot be assigned DESB quantum numbers unambiguously. We also investigate these quantum numbers for states of 1S even parity in He. We find two types of mixing of DESB states in the doubly excited states calculated. We also show that the amount of mixing of DESB quantum numbers can be inferred from the value of the cosine of the inter-electronic angle. In a study on Li- the calculated cosine values are used to identify doubly excited states measured in a photodetachment experiment. In particular a resonant state that violates a propensity rule is found.

Neste trabalho elaboramos estudos teóricos sobre colisões frias mediadas por fótons em armadilhas magnéto-ópticas. Para isto implementamos algorítimos numéricos de alto desempenho para o cálculo das formas de linha do espectro de fotoassociação do 88Sr. O principal algorítimo utilizado foi o de Numerov renormalizado. Também foram implementados sistemas de construção dos elementos da matriz hamiltoniana para estudos de colisões atômicas levando em consideração a estrutura fina dos potenciais de interação. Por último introduzimos o método de Monte Carlo de Integrais sobre Trajetórias como ferramenta para o estudo da termodinâmica do condensado de Bose-Einstein em armadilhas 2D considerando a interação entre os átomos / In this work we present theoretical studies of cold collisions mediated by photons in magneto-optical traps. We have implemented high-performance numerical algorithms to calculate the photoassociation spectral line shapes of 88Sr. We have mainly utilized the renormalized Numerov algorithm. We have also implemented schemes to write down the Hamiltonian matrix elements to study atomic collisions taking into account the fine structure of the interaction potentials. Finally, we have introduced the Path Integral Monte Carlo method as a tool for studying the thermodynamics of the Bose-Einstein condensate in two-dimensional traps, considering the binary atomic interactions

Neste trabalho resultados experimentais inéditos da taxas de perdas para o sistema Cs-K em função da intensidade do laser de aprisionamento foram obtidos. A análise dos resultados foi auxiliada pelo modelo tipo Gallagher-Pritchard que demonstrou possuir uma dependência muito forte com a velocidade de escape. Um estudo complementar ajudou na determinação dos mecanismos causadores de perdas, a catálise óptica, onde o principal resultado foi a obtenção de um resultado teórico que corresponde a observação experimental para o sistema Na-Rb, onde as perdas foram associadas a atuação do estado duplamente excitado. Compreender os mecanismos causadores de perdas pode ajudar na construção de armadilhas magneto-ópticas de grande eficiência, importantes em experimentos de medidas de propriedades atômicas. / We have investigated trap loss rate as a function of trap laser intensity for the Cs-K system. A model based on Gallagher-Pritchard type considerations, allow understand the obtained results. To correctly interpret the data, we have proposed new mechanisms, which can be proven with recent experiment in Na-Rb system.

<p dir="ltr">Complex physical systems provide a fertile ground for exploring various phenomena owing to the quantum nature inherent in their structure. Atoms and molecules not only serve as realistic systems for experimental investigation, but also exhibit a complexity stemming from their many-body interactions which is of significant theoretical interest. This thesis delves into the domain of ultracold collisions between different interacting species (where temperature T < 1mK), and introduces novel applications for probing such systems, particularly focusing on molecular formation via photoassociation. Molecular interactions, in comparison to their atomic counterparts, present heightened complexity. The interplay of electrostatic forces among electrons and nuclei intricately couples all degrees of freedom within a single molecule. Historically, the exploration of quantum dynamics between molecules was pioneered by Born and Oppenheimer. Their seminal work involved solving Schrödinger’s equation in two steps. First step is addressing a portion of the molecular Hamiltonian where the nuclei are clamped in space (adiabatic). This adiabatic solution yields effective potentials between nuclei, encapsulating the integrated influence of the surrounding electronic cloud. The second step is to solve for the nuclear degrees of freedom in the vicinity of the effective potentials. The validity of the Born-Oppenheimer approximation stems from the substantial mass disparity between electrons and nuclei, enabling a quasi-separation of the electronic and nuclear Hamiltonians. The first order Born-Oppenheimer approximation assumes a partial separation of the molecular wave function Ψmolecule ≈ ΞvibrationYrotationalΦelectronic.</p><p dir="ltr"> A comprehensive treatment is provided for systems with numerous degrees of freedom, elucidating how the Born-Oppenheimer approximation manifests when applied to molecules. This chapter also encapsulates the principal findings from collision theory and photoassociation spectroscopy, as well as foundational techniques underpinning this thesis. Spectroscopic investigations encompass four relevant transition types: boundbound (Rabi oscillations), bound-free (photoionization), free-free (elastic scattering), and free-bound (photoassociation) transitions. Photoassociation (PA) spectroscopy probes laserinduced processes where the reactants interact through a channel |i〉, and can absorb one or more photons causing a transition to a bound state in an excited channel |f〉. The excited complex usually decays with a high probability to the ground state of the formed molecule. The same process can be utilized experimentally to prepare a cold molecule in its vibrational ground state . Diatomic PA has been of great theoretical and experimental interest in recent years. Herein, we present a theoretical inquiry into photoassociation within triatomic systems, with a particular focus on alkali atom-dimer systems, and introduce a method for calculating PA rates.</p><p dir="ltr">Moreover, this thesis presents different methods for shielding polar molecules from their short-range interactions where inelastic collisions and chemical reactions can occur with high probability. Shielding polar molecules has been shown to suppress inelastic collisions substantially between two molecules. A technique to shield two polar molecules in their ground state is studied and applied to model collisions in a gas of ground state (NaCs) molecules at temperatures T ≈ 100nK. The results show a region of interactions between two polar molecules that has an extremely long-range nature and is well isolated from the short-range losses, allowing for long-range spectroscopic studies. A new long-range regime of molecular physics arises in the study of shielded molecules where long-range vibrational tetramer states form. Different tetramer formation pathways are studied within a range of different shielding parameters. In fact, microwave shielding provides a region to study collisions between polar molecules, and controls their dynamics without worrying about shortrange losses. It has also been applied in the observation of a Bose gas of polar molecules.</p>

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.

In this thesis, the effects of simple shear flow on macromolecular structure and interactions are investigated in detail via a combination of Nuclear Magnetic Resonance (NMR) spectroscopy and rheology, namely Rheo-NMR. A specially designed NMR couette shear cell and benchtop shear cell, developed in-house, demonstrated that the direct measurement of the above phenomena is possible. First, to determine whether the shear cells were creating simple shear flow, results were reproduced from literature studies of liquid crystal systems which report shear effects on: Cetyl Trimethyl Ammonium Bromide (CTAB) in deuterium oxide, and Poly(gamma-benzyl-L-glutamate) (PBLG) in m-cresol. Next, the possible conformational changes to protein structure brought about by shear were investigated by applying shear to Bovine -lactogobulin ( -Lg). As the protein was sheared, a small, irreversible conformational change was observed by means of one-dimensional and two-dimensional 1H NMR with reasonable reproducibility. However, no observable change was detected by means of light scattering. A large conformational change was observed after shearing a destabilized -Lg sample containing 10% Trifluoroethanol (TFE) (v/v). From an NMR point of view, the sheared state was similar to the structure of -Lg containing large amounts of -helices and, interestingly, similar to the structure of -Lg containing -sheet amyloid fibrils. Gel electrophoresis tests suggested that the changes were caused by hydrophobic interactions. Unfortunately, this proved to be difficult to reproduce. The effect of shear on an inter-macromolecular interaction was investigated by applying shear during an enzyme reaction of pectin methylesterase (PME) on pectin. Experimental method and analysis developments are described in detail. It was observed that under the conditions studied, shear does not interfere with the de-esterification of pectin with two types of PME, which have different action mechanisms at average shear rates up to 1570 s-1.