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Radiative processes of small molecules
Šimsová, Martina ; Soldán, Pavel (advisor) ; Čurík, Roman (referee) ; Kalus, René (referee)
Four types of astrochemically relevant radiative processes are studied: bound-bound, bound-free, free-bound and free-free. The former two together determine radiative lifetimes, which are calculated for the HeLi+ molecular ion. Free-bound processes, also called radiative association, are studied on two systems: He in collisions with Li+ , and O in collision with C+. Collisions of He and Li+ are believed to have occurred during the recombination era of the Universe, while collisions of O with C+ are considered to be relevant in SN 1987A. Altogether, 17 radiative association cross sections and rate coefficients are calculated for radiative association, and the effect of a stimulated emission is also illustrated. A free-free process, also called radiative charge transfer, is studied in collisions of He with Li+.
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Modelling of Ultracold Gases in Multidimensional Optical Lattices
Urbanek, Miroslav ; Soldán, Pavel (advisor) ; Opatrný, Tomáš (referee) ; Veis, Libor (referee)
Title: Modelling of Ultracold Gases in Multidimensional Optical Lattices Author: Miroslav Urbanek Department: Department of Chemical Physics and Optics Supervisor: doc. Ing. Pavel Soldán, Dr. Abstract: Optical lattices are experimental devices that use laser light to confine ultracold neutral atoms to periodic spatial structures. A system of bosonic atoms in an optical lattice can be described by the Bose-Hubbard model. Although there exist powerful analytic and numerical methods to study this model in one dimension, their extensions to multiple dimensions have not been as successful yet. I present an original numerical method based on tree tensor networks to simulate time evolution in multidimensional lattice systems with a focus on the two-dimensional Bose-Hubbard model. The method is used to investigate phenomena accessible in current experiments. In particular, I have studied phase collapse and revivals, boson expansion, and many-body localization in two-dimensional optical lattices. The outcome of this work is TEBDOL - a program for modelling one-dimensional and two-dimensional lattice systems. Keywords: Bose-Hubbard model, multidimensional system, optical lattice, tensor network
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Quantum dynamics of small molecules
Augustovičová, Lucie ; Soldán, Pavel (advisor) ; Čurík, Roman (referee) ; Fišer, Jiří (referee)
This thesis deals with the process of molecular ions formation in interstellar space, which played an important role in the early Universe. A large part of the work focuses on the theoretical study of quantum dynamics of the process of radiative association pre- dominantly induced by dipole transitions. The effect of quadrupole transitions on the radiative association have also been taken into account, which has been studied for the first time. Furthermore, spectroscopic characteristics of rovibronic transitions of selected di- atomic ions for the study of cosmological variability of fundamental constants were determined. The main outcomes of the thesis include the characterization of depopulation of metastable levels He (23S) and He (21S) due to radiative collisions with hydrogen, helium and lithium ions, i. e. He + A+ → HeA+ + hν. Within the study quantum dynamics calculations were carried out using a fully quan- tal approach. Studied spontaneous and stimulated processes on a specific spin manifold were characterized by energy-dependent cross sections and temperature-dependent rate coefficients. Compared to previous published works by other authors highly excited electronic states are considered. The results showed that a) the spontaneous radiative association contributes significantly to the...
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Studium biologicky relevantních systémů v elektronicky excitovaných stavech
Zámečníková, Martina ; Soldán, Pavel (advisor) ; Bludský, Ota (referee) ; Nachtigallová, Dana (referee)
Very short lifetimes of excited states of isolated bases in nucleic acids, on the picosec- ond order, are believed to contribute to photostability of the genetic code. When embedded in DNA this behavior becomes more complex, mainly due to their inter- actions via stacking and hydrogen bonding. The DNA photophysiscs is not fully understood yet. It depends e.g. on the conformation and the character of excited states. The studies on smaller systems can help to improve the understanding of these phenomena. The aim of this work was to examine the dynamics of the excited states of the n → π∗ character of the complex of N-methylformamide dimer and two waters. The study was performed using non-adiabatic dynamics simulations with on-the-fly Surface Hopping algorithm based on the potential energy surfaces and non-adiabatic couplings obtained with multi-reference approach. The results show that after the vertical excitation into delocalized S2 state the system relaxes into S1 state within several tens femtoseconds. For majority of the population, the charac- ter of the state then oscillates between localized and delocalized during the whole course of the dynamics. Comparison with calculations with the waters removed in- dicates that the delocalization is caused by waters serving as a bridge between the two chromophores. 1
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