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Dynamics of ultrafast processes in excited states of organic and inorganic compounds / Dynamique de processus ultra-rapides dans les états éxcités de composés organiques et inorganiquesEng, Julien 25 September 2015 (has links)
Les travaux présentés dans cette thèse peuvent être divisés en deux parties. Dans une première partie, nous avons étudié le processus de photoisomérisation dans plusieurs systèmes. Une analyse de structure électronique accompagnée d’un calcul préliminaire de dynamique semi-classique ont été appliqué à un modèle minimal du rétinal afin d’extraire les degrés de libertés les plus importants lors de l’isomérisation. Cela dans le but de construire des surfaces d’énergie potentielle diabatiques pour effectuer une étude de dynamique quantique. Une approche de type dynamique semi-classique a été appliquée à un modèle de moteur moléculaire dans le but d’étudier l’origine de l’uni-directionalité de sa rotation. Finalement, une étude de structure électronique d’un complexe de Rhénium contenant un ligand de type rétinal a été effectué pour étudier l’influence du métal sur la spectroscopie du ligand rétinal. Dans une deuxième partie nous nous sommes intéressés à l’étude des croisements intersystème dans un complexe de Rhénium. Afin de pouvoir apporter une explication à un comportement contrintuitif de ce complexe, nous avons développé un Hamiltonien modèle capable de tenir compte des couplages vibroniques interétats et spin-orbit. Cet Hamiltonien a été testé sur ce-dit système, et nous a permis, grâce à une étude de structure électronique de proposer un mécanisme de relaxation différent de celui proposé expérimentalement. / This thesis can be divided in two parts.In the first one, we have studied the photoisomerization process in several systems. An electronic structure analysis mixed with a preliminary semi-classical dynamics investigation has been applied to a minimal model of the retinal chromophore in order to select the most important degrees of freedom involved in the process. The goal of this is to build diabatic potential energy surfaces in order to conduct quantum dynamics simulations. A semi-classical approach has also been applied to a molecular motor model to study the origin of the unidirectionality of its rotary motion. Finally, an electronic structure of a rhenium complex with a retinal-like ligand has been performed to study the effect of the coordination to a metallic atom on the spectroscopy of the retinal ligand. In the second part, we have investigated the intersystem crossings in a rhenium complex. In order to bring an explanation to an experimentally observed conterintuitive behavior of this complex, we have developed a model Hamiltonian that includes both interstate vibronic coupling and spin-orbit coupling. This Hamiltonian has been tested on the said complex and, in complement to an electronic structure study, allowed us to formulate a decay mechanism different from the one proposed based on experiments.
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Chemical Reaction Dynamics at the Statistical Ensemble and Molecular Frame LimitsClarkin, OWEN 12 September 2012 (has links)
In this work, experimental and theoretical approaches are applied to the study of chemical reaction
dynamics. In Chapter 2, two applications of transition state theory are presented: (1) Application of
microcanonical transition state theory to determine the rate constant of dissociation of C2F3I
after π∗ ← π excitation. It was found that this reaction has a very fast rate constant
and thus
is a promising system for testing the statistical assumption of molecular reaction dynamics. (2) A general
rate constant expression for the reaction of atoms and molecules at surfaces was derived within the statistical
framework of flexible transition state theory.
In Chapter 4, a computationally efficient TDDFT approach was found to
produce useful potential energy surface landscapes for application to non-adiabatic predissociative dynamics
of the molecule CS2 after excitation from the ground state to the singlet C-state. In Chapter 5, ultrafast
experimental results of excitation of CS2 to the predissociative neutral singlet C-state is presented. The
bandwidth of the excitation laser was carefully tuned to span a two-component scattering resonance with each
component differently evolving electronically with respect to excited state character during the quasi-bound
oscillation. Scalar time-resolved photoelectron spectra (TRPES) and vector time-resolved photoelectron
angular distribution (TRPAD) observables were recorded during the predissociation. The TRPES yield of
photoelectrons was found to oscillate with a quantum beat pattern for the photoelectrons corresponding to
ionization to the vibrationless cation ground state; this beat pattern was obscured for photoelectron energies
corresponding to ionization from the vibrationally excited CS2 cation. The TRPAD data was recorded for
two general molecular ensemble cases: with and without a pre-excitation alignment laser pulse. It was found
that in the case of ensemble alignment (Chapter 6), the “molecular frame” TRPAD (i.e. TRMFPAD) was
able to image the purely valence electronic dynamics of the evolving CS2 C-state. The unaligned ensemble
TRPAD observable suffers from excessive orientational averaging and was unable to observe the quantum
beat.
Engineering efforts were also undertaken to eliminate scattered light background signal (Chapter 7,
Appendix A) and improve laser stability as a function of ambient pressure (Appendix B) for TRMFPAD
experiments. / Thesis (Ph.D, Chemistry) -- Queen's University, 2012-09-11 22:18:20.89
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