In this thesis, we present a theoretical investigation of reactive processes involving the HeH$^+$ molecular ion, with applications in laboratory and astrophysical plasma physics. We consider in particular two processes, which are the charge transfer in H + He$^+$ collisions at low energy from a molecular approach and the photodissociation of HeH$^+$. At the molecular level, the cross section is the basic quantity that has to be determined in order to achieve an understanding of reactive processes. Its calculation will be based on the description of the reactions using an emph{ab initio}, quantum mechanical approach. In this work, we will rely on the Born-Oppenheimer approximation, which allows the molecular motion to be separated into an electronic and a nuclear motion. The evaluation of cross sections then follows two steps. The first is the determination of the electronic structure of the molecule. We will calculate the adiabatic potential energy curves of the excited electronic states as well as the dipole matrix elements between these states. The non-adiabatic radial and rotational couplings, which result from the breakdown of the Born-Oppenheimer approximation, are also estimated. The second step is to solve the nuclear motion, which we achieve using a time-dependent method based on the propagation of wave packets on the coupled electronic states. A particular emphasis will be put on the importance of the excited states and of the non-adiabatic couplings in the description of reactive processes. In the treatment of the charge transfer reaction between H and He$^+$ in excited states, it is well known that the non-adiabatic radial couplings cannot be neglected. However, we will show that the inclusion of the non-adiabatic rotational couplings is also necessary in order to obtain accurate state-to-state cross sections. In the description of the photodissociation of HeH$^+$ from its ground state, we will show the influence of the excited states on the rate constant and the role of the non-adiabatic radial couplings in the determination of partial cross sections. We will also consider the possible astrophysical applications of the first triplet state of HeH$^+$. We will show that this state is metastable by evaluating its lifetime, and calculate the cross sections and rate constants for the photodissociation and radiative association of HeH$^+$ in this state.

No description available.

In any quantum dynamics method that approximates wave functions as a linearly combined basis set, non-orthogonality can be is a problem. It has been proven in previous studies that, by using the most standard form of Matching Pursuit in combination with a Gaussian wave packet ansatz, exact quantum-mechanical correspondence can be obtained for particle tunneling in one and two dimensions. This study is an attempt to prove that this approach can be generally applicable to systems of arbitrary dimension propagating with an an-harmonic potential, and that adaptive initial state sampling can be used to make the method even more computationally efficient.

Orientador: Marcelo Moraes Guzzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-06T18:58:44Z (GMT). No. of bitstreams: 1 Torres_FernandoRossi_M.pdf: 2093943 bytes, checksum: 598961cdc3d39df5a3ff30060070d443 (MD5) Previous issue date: 2006 / Resumo: Em geral, estudamos o fenômeno de oscilação de neutrinos através do formalismo de ondas planas, que consegue, com muito sucesso, tratar os casos dos neutrinos solares, de reatores e aceleradores. No entanto, uma descrição física mais completa deve considerar a interpretação do fenômeno oscilatório usando pacotes de onda. Neste trabalho, analisamos o formalismo das ondas planas e dos pacotes de onda na oscilação, tanto no vácuo quanto na matéria. Calculamos os comprimentos de coerência e oscilação para discutir a necessidade ou não da utilização de pacotes de onda para neutrinos solares, neutrinos de reatores e de aceleradores, neutrinos de supernovas e neutrinos de altíssima energia. Discutimos também o mecanismo de formação de supernovas e o papel dos neutrinos na dinâmica de sua evolução. Como temos poucas informações sobre neutrinos de supernova, apenas 11 eventos detectados por Kamiokande e 8 eventos pelo detector IMB, confrontamos o formalismo de ondas planas com o formalismo de pacotes de onda para a oscilação de neutrinos dentro de uma supernova de 15 massas solares, com o intuito de saber a relevância dos pacotes de onda e verificar se este formalismo pode fornecer alguma informação adicional sobre a oscilação de neutrinos em supernovas / Abstract: Generally, we study neutrino oscillation phenomenon using the plane wave formalism, which successfully treats the solar neutrino case, the reactor and accelerator cases. However, a more complete description of neutrino oscillation must consider a wave packet approach. This work analyses both formalisms: the plane wave and the wave packet in vacuum and matter. We have calculated the oscillation and coherence length to discuss if wave packets are or are not necessary for solar neutrinos, reactor and accelerators neutrinos, supernova neutrinos and ultra-high energy neutrinos. We also have discussed the formation mechanism of supernova and the role of neutrinos in its evolution dynamics. As we have little information about supernova neutrinos, only 11 events detected by Kamiokande and 8 events by IMB detector, we have confronted the plane wave formalism with the wave packet formalism of neutrino oscillation inside a supernova with 15 solar masses, because we desire to know the relevance of the wave packet treatment and verify if this formalism will provide any additional information about neutrino oscillation in supernova / Mestrado / Física das Particulas Elementares e Campos / Mestre em Física

In this thesis, we present a theoretical investigation of reactive processes involving the HeH$^+$ molecular ion, with applications in laboratory and astrophysical plasma physics. We consider in particular two processes, which are the charge transfer in H + He$^+$ collisions at low energy from a molecular approach and the photodissociation of HeH$^+$.<p><p>At the molecular level, the cross section is the basic quantity that has to be determined in order to achieve an understanding of reactive processes. Its calculation will be based on the description of the reactions using an emph{ab initio}, quantum mechanical approach. In this work, we will rely on the Born-Oppenheimer approximation, which allows the molecular motion to be separated into an electronic and a nuclear motion. The evaluation of cross sections then follows two steps.<p>The first is the determination of the electronic structure of the molecule. We will calculate the adiabatic potential energy curves of the excited electronic states as well as the dipole matrix elements between these states. The non-adiabatic radial and rotational couplings, which result from the breakdown of the Born-Oppenheimer approximation, are also estimated. The second step is to solve the nuclear motion, which we achieve using a time-dependent method based on the propagation of wave packets on the coupled electronic states. <p><p>A particular emphasis will be put on the importance of the excited states and of the non-adiabatic couplings in the description of reactive processes. <p>In the treatment of the charge transfer reaction between H and He$^+$ in excited states, it is well known that the non-adiabatic radial couplings cannot be neglected. However, we will show that the inclusion of the non-adiabatic rotational couplings is also necessary in order to obtain accurate state-to-state cross sections.<p>In the description of the photodissociation of HeH$^+$ from its ground state, we will show the influence of the excited states on the rate constant and the role of the non-adiabatic radial couplings in the determination of partial cross sections.<p>We will also consider the possible astrophysical applications of the first triplet state of HeH$^+$. We will show that this state is metastable by evaluating its lifetime, and calculate the cross sections and rate constants for the photodissociation and radiative association of HeH$^+$ in this state.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21369号 / 工博第4528号 / 新制||工||1705(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 中村 裕之, 教授 安田 秀幸 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Bhom's hydrodynamic formulation (or quantum fluid dynamics) is an attractive approach since, it connects classical and quantum mechanical theories of matter through Hamilton-Jacobi (HJ) theory, and quantum potential. Lopreore and Wyatt derived and implemented one-dimensional quantum trajectory method (QTM), a new wave-packet approach, for solving hydrodynamic equations of motion on serial computing environment. Brook et al. parallelized the QTM on shared memory computing environment using a partially implicit method, and conducted accuracy study of a free particle. These studies exhibited a strange behavior of the relative error for the probability density referred to as the transient effect. In the present work, numerical experiments of Brook et al. were repeated with a view to identify the physical origin of the transient effect and its resolution. The present work used the QTM implemented on a distributed memory computing environment using MPI. The simulation is guided by an explicit scheme.

No description available.

This thesis explores the dynamics of a heteronuclear diatomic molecular ion, possessing a permanent electric dipole moment, µ, which is trapped in a linear Paul trap and can interact with an off-resonance laser field. To build our model we use the rigid-rotor approximation, where the dynamics of the molecular ion are limited to its translational and rotational motions of the center-of-mass. These dynamics are investigated by carrying out suitable numerical calculations. To introduce our numerical methods, we divide our research topic into two different subjects. First, we ignore the rotational dynamics of the ion by assuming µ = 0. By this assumption, the system resembles an atomic ion, which mainly exhibits translational motion for its center of the mass when exposed to an external trapping field. To study this translational behavior, we implement full-quantum numerical simulations, in which a wave function is attributed to the ion. Finally, we study the quantum dynamics of the mentioned wave packet and we compare our results with those obtained classically. In the latter case, we keep the permanent dipole moment of the ion and we study the probable effects of the interaction between the dipole moment and the trapping electric field, on both the translational and the rotational dynamics of the trapped molecular ion. In order to study these dynamics, we implement both classical and semi-classical numerical simulations. In the classical method, the rotational and the translational motions of the center of mass of the ion are obtained via classical equations of motion. On the other hand, in the semi-classical method, while the translational motion of the center-of-mass is still obtained classically, the rotation is treated full-quantum mechanically by considering the rotational wave function of the ion. In the semi-classical approach, we mainly study the probable couplings between the rotational states of the molecular ion, due to the interaction of the permanent dipole moment with the trapping electric field. In the end, we also present a semi-classical model, where the trapped molecular ion interacts with an off-resonance laser field.

<p>In this thesis I have theoretically studied electron recombination processes with small molecular ions.</p><p>In these kind of processes resonant states are involved. To calculate the potential energy for these states as a function of internuclear distance, structure calculations and scattering calculations have to be performed.</p><p>So far I have been studying the ion-pair formation with in electron recombination with H₃⁺. The cross section for this process has been calculated using different kind of models, both a time dependent quantum mechanical and a semiclassical.</p><p>I have also studied the direct process of dissociative recombination of HF⁺. To calculate the total cross section for this process, we have performed wave packet propagation on thirty resonant states and summed up the individual cross sections for these states.</p><p>The cross sections for both these processes have a similar appearance to those measured experimentally in the ion storage ring CRYRING in Stockholm.</p>