Due to the fast increasing capabilities of modern computers it is now feasible to calculate spectra of small atom and molecules with the greater level of accuracy than high-resolution measurements. The mathematical algorithms developed and implemented on high performance supercomputers for the quantum mechanical calculations are directly derived from the first principles of quantum mechanics. The codes developed are primarily used to verify, refine, and predict the energies associated within a given system and given angular momentum state of interest. The Hamiltonian operator used to determine the total energy in the approach presented is called the internal Hamiltonian and is obtained by rigorously separating out the center-of-mass motion (or the elimination of translational motion) from the laboratory-frame Hamiltonian. The methods utilized in the articles presented in this dissertation do not include relativistic corrections and quantum electrodynamic effects, nor do these articles assume the Born-Oppenheimer (BO) approximation with the exception of one publication. There is one major review article included herein which describes the major differences between the non-BO method and the BO approximation using explicitly correlated Gaussian (ECG) basis functions. The physical systems studied in this dissertation are the atomic elements with Z < 7 (although the discussion is not limited to these) and diatomic molecules such as H₂⁺ and H₂ including nuclear isotopic substitution studies with deuterium and tritium, as well as electronic substitutions with the muon particle. Preliminary testing for triatomic molecular functionals using a model potential is also included in this dissertation. It has been concluded that using all-particle ECGs with including the addition of nonzero angular momentum functions to describe nonzero angular momentum states is sufficient in determining the energies of these states for both the atomic and molecular case.

The interaction between high-n Rydberg states of molecular hydrogen and metal surfaces has been investigated for the first time. Rydberg states of hydrogen possessing either 0 or 2 units of rotational angular momentum, defined by the quantum number N⁺ , and principal quantum numbers in the range n= 17 22 (for the N⁺= 2 states) and n=41-45 (for the N⁺= 0 states) are directed at a grazing angle onto a metal surface (gold or aluminium). At a sufficiently close distance ionisation may occur via tunnelling of the Rydberg electron into the vacant metal conduction band. Any ions formed in the vicinity of the metal are extracted by the application of an electric field and information about the distance at which the ions are formed can be inferred from the magnitude of the applied field required for detection. Two novel effects are observed. Firstly, it appears that the rotation of the H2⁺ core has a significant effect on the ionisation properties of the Rydberg states in a manner akin to rotational autoionisation, such that the rotational energy of the core is given up to the Rydberg electron. Secondly, the surface ionisation profiles do not vary smoothly with applied field suggesting that at certain fields the feasibility of ionisation is either enhanced or reduced. A preliminary discussion of the origin of the structure is presented in terms of the crossings in the Stark map between the N⁺= 0 and N⁺= 2 Stark manifolds. The development of a theoretical model, and an associated Fortran program, involving the technique of complex scaling is also reported. The hydrogen molecules are modeled using an atomic hydrogen system which provides a good first approximation to the behaviour of the Rydberg electron for states with n > 5. Energies and linewidths, for states with principal quantum number n= 6 9 interacting with a model surface, are explicitly calculated at a range of surface separations. From this information, predictions of the ionisation behaviour expected for states of higher principal quantum number are presented.

No description available.

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 163-)

Universiẗat, Diss., 1999--Freiburg (Breisgau).

Th.--Sci. phys.--Grenoble 1, 1983. N°: 11. / Extr. en partie du Journal de physique, 41, 1980, 819-830 ; de Journal of physics. B, Atomic and molecular physics, 11, 1978, 22, 3875-3886 et de Journal of chemical physics, 72, 1980, 12. 6698-6705.

No description available.

Neste trabalho estudamos a interação entre átomos de Rydberg no estado nP e sua dependência com o campo elétrico dc. Estes estados apresentam ressonâncias Föster para um número quântico principal n menor que 37. Nestes processos de ressonância um par atômico no estado nP muda para um par nS+(n+1)S. Realizamos dois experimentos de evolução temporal para 32&le;n&le;36. No primeiro investigamos a dependência da taxa de transferência de população NnS em função do número quântico principal n. E no segundo estudamos a transferência de população para um estado fixo de n=33 em função do campo elétrico. Além disso, estudamos a dependência da população no estado 33S em função da densidade de átomos de Rydberg no estado 33P. Estes resultados nos permitem observar duas contribuições distintas, uma linear relacionada a radiação de corpo negro e uma quadrática ligada a interação de dois corpos. Estes resultados confirmam o modelo de taxa para o efeito da radiação de corpo negro. / In this work we studied the role of Rydberg atoms interactions in the nP state and the dc electric field dependency of this process. The nP state shows Föster resonances for principal quantum number less than 37. In this resonance process, an atomic pair in nP state changes to a pair nS+(n+1)S. We have performed two time evolution experiments for 32&le;n&le;36. In the first one we have investigated the NnS population transfer rate for a variable principal quantum number n. In the second we have study the population transfer for a fixed n=33, by varying an electric field. Moreover, we observed the density dependency of the population in the 33S state by varying the nP state atomic density. The results allow us to observe two distinct contributions, a linear contribution related with the black body radiation and a quadratic one connected with two body process. The results agree well with the rate model used to treat the black body radiation.

Orientador: Marcus Aloizio Martinez de Aguiar / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-20T03:44:40Z (GMT). No. of bitstreams: 1 XavierJunior_AdemirLuiz_M.pdf: 2024884 bytes, checksum: 42deb17795a8caac1e9650699e6bd935 (MD5) Previous issue date: 1993 / Resumo: Neste trabalho, o limite semiclássico e clássico de uma partícula sujeita ao potencial l/r é tratado. Fazemos um estudo do fenômeno de Revivals quânticos usando funções especiais localizadas no regime de grandes números quânticos (princípio de correspondência). Estes estados representam uma partícula evoluindo sobre uma órbita circular . O comportamento clássico, representado por órbitas de excentricidade arbitrária, é obtido pela aplicação da transformação regularizadora de Kustaanheimo-Stiefel. Tal transformação possibilita a definição de pacotes de onda formalmente idênticos aos estadis coerentes de um oscilador harmônico. Algumas questões relacionadas com a redefinição do parâmetro temporal pela introdução de um tempo fictício são discutidas. Uma expressão formal de conexão entre as funções de onda paramétricas geradas pela transformação e as funções reais é obtida via integração de trajetória. Por fim, retomamos o estudo dos estados coerentes e o comportamento clássico é derivado na forma da equação do movimento ( equação de Kepler ), onde fica possível associar o tempo fictício com a anomalia excêntrica do movimento. A introdução da dependência com a energia da frequência própria das funções componentes do estado coerente possibilita, no limite de níveis contínuos, aprova da decoerência desses estados que possuem uma estrutura apenas formalmente similar aos verdadeiros estados coerentes / Abstract:In this work, the semiclassical and classicallimit of a particle subjected to the l/r potential is treated. We study the quantum revival fenomenon using special localized functions in the large quantum number regime ( correspondence principle ). These states correspond to an electron evolving on a circular orbit in a higly excited Hydrogen atom. The classical behavior represented by orbits with arbitrary excentricity is obtained by applying the regularized Kustaanheimo-Stiefel transformation in its quantum version. This transformation makes possible the definition of wave packets formaly identical to the harmonic oscillator coherent states. Some questions related to the definition of a new temporal parameter, the so ca1led fictitious time, are discussed. A formal conection formula, between the parametric wave functions generated by the transformation and the real wave functions, is proposed. Fina1ly, we go back to the coherent hydrogen states in two dimensions and the classical behavior is derived in the form of the Kepler equation.It is then possible to associate the fictitious time parameter with the eccentric anomaly for the motion. The introduction of the energy dependent frequency in the quantum evolution gives, in the limit of continuum levels, the proof of a irreversible decoherence of these pseudo-coherent states which have a structure only formaly similar to the truly coherent states / Mestrado / Física / Mestre em Física

L’étude comparée des réactions de formation de paires d’ions et de simple photoionisation de la molécule NO2 induites par rayonnement synchrotron (RS) d’une part et par impulsions laser femtosecondes (fs) d’autre part, démontre le rôle remarquable de l’excitation résonante d’états de Rydberg dans la dynamique électronique et nucléaire induite. Trois réactions principales, la photoionisation non dissociative (NO2+ (X 1Σ+g) + e), la photoionisation dissociative (NO+ (X 1Σ+) + O(3P) + e) et la formation de paires d'ions, (NO+ (X 1Σ+) + O- (2P)), ont été caractérisées en utilisant la méthode des corrélations vectorielles ou spectroscopie en coïncidence des impulsions du photoélectron et des photoions, auprès des sources RS (SOLEIL, DESIRS) et lasers fs (CEA, Saclay), respectivement. Le diagramme de corrélation des énergies cinétiques électron-ion, première observable issue de ces mesures, met en évidence un partage de l’énergie en excès entre noyaux et électrons qui dépend fortement du mode d’excitation photonique. Les déviations significatives observées par rapport aux profils d’ionisation de type Franck Condon sont attribuées à des couplages vibroniques entre états excités NO2*, tels que ceux induits par une intersection conique. Les chemins réactionnels identifiés confirment le rôle de l’excitation des séries de Rydberg [R*(6a1)-1] et [R*(4b2)-1] intervenant comme états intermédiaires dans l’excitation multiphotonique ou dans le continuum d’ionisation exploré. Une étude complémentaire par spectroscopie à haute résolution des états [R*(6a1)-1] a été mise en œuvre (UBC, Vancouver).Pour une réaction de photoionisation dissociative (PID), l’observable la plus complète est la distribution angulaire des photoélectrons dans le référentiel lié à la vitesse de recul de l’ion fragment (RFPAD) déduite de la mesure de la corrélation vectorielle (Vi, Ve, P). Afin d’accéder aux éléments de matrice dipolaire décrivant la photoionisation de l’état électronique considéré, le formalisme développé en collaboration avec R. R. Lucchese (Texas A&M) décrivant la photoémission dans le référentiel moléculaire pour la simple PID d'une molécule linéaire par excitation à un photon, a été étendu à l'étude des réactions de PID par excitation multiphotonique d'une molécule polyatomique, telle que la molécule NO2 de symétrie C2v. L’analyse multivariée de la RFPAD multiphotonique proposée constitue une stratégie fructueuse en vue d’extraire l’information optimale sur la dynamique complexe de photoionisation et de réaliser une comparaison détaillée entre les résultats expérimentaux et les calculs de photoionisation des états excités de la molécule. / The comparative study of ion pair formation and simple photoionization of the NO2 molecule induced by synchrotron radiation (SR) on the one hand and by femtosecond (fs) pulses on the other hand reveals the remarkable role of Rydberg states in the induced electronic and nuclear dynamics. Three main reactions, namely (NO2+ (X 1Σ+g) + e) non dissociative photoionization, (NO+ (X 1Σ+) + O(3P) + e) dissociative photoionization and (NO+ (X 1Σ+) + O- (2P)) ion pair formation have been characterized using the vector correlation method, or photoion and photoelectron coincidence momentum spectroscopy, at SR sources (SOLEIL DESIRS) and at fs laser platforms (CEA, Saclay), respectively. The electron-ion kinetic energy correlation diagram, which is the first observable obtained from these measurements, highlights the excess energy sharing among nuclei and electrons, which strongly depends on the photon excitation mode. The observed remarkable deviations from Franck Condon ionization profiles are attributed to vibronic couplings such as those induced at a conical intersection. The identified reaction pathways confirm the role of the [R*(6a1)-1] and [R*(4b2)-1] Rydberg series excitation as stepping states in multiphoton excitation or in the explored ionization continua. A complementary study of high resolution spectroscopy of [R*(6a1)-1] Rydberg series has been performed (UBC, Vancouver). For a dissociative photoionization (DPI) process, the most complete observable is the photoelectron angular distribution in the reference frame attached to the recoil ion fragment velocity (RFPAD) deduced from the measured (Vi, Ve, P) vector correlation. In order to get access to the dipole matrix elements describing photoionization of the considered excited electronic state, the formalism developed in collaboration with R. R. Lucchese (Texas A&M) describing molecular frame photoemission for a DPI of a linear molecule by one-photon excitation has been extended to the study of DPI processes induced by multiphoton excitation for a polyatomic molecule, such as the NO2 molecule of C2v symmetry. The proposed multivariate analysis of the multiphoton RFPAD constitutes a successful strategy to extract the optimal information on the complex photoionization dynamics and to perform a detailed comparison between experimental results and calculations of photoionization of the molecular excited states.