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Previous issue date: 2016-06-08 / Esta tese dedicada a estudos tericos e experimentais de espalhamento ressonante inelstico
de raios-X (Resonant inelastic X-ray scattering - RIXS) de molculas de monxido de carbono
e gua em fase gasosa. Usando estado da arte clculos ab initio de estrutura eletrnica e formalismo
de pacotes de onda dependente do tempo, uma anlise completa dos espectros RIXS
experimental dos dois sistemas moleculares foi realizada. Na anlise do CO RIXS, fomos
capazes de reproduzir o experimento RIXS com excelente preciso, permitindo uma descrio
completa dos espectros experimentais. Interferncia entre diferentes canais RIXS correspondentes
disperso via orbitais moleculares ortogonais no estado excitado do CO descrito.
Com a ajuda do espectro de alta resoluo e simulaes ab initio, mostramos a quebra da aproximao
de Born-Oppenheimer na regio onde estados nais de Rydberg acoplam com o estado
nal de valncia. Explicamos a formao de uma caracterstica espectral, que foi atribuda a
um nico estado em estudos anteriores. Alm disso, atravs da combinao experimento-teoria,
aprimoramos o mnimo do potencial do estado excitado de valncia E 1 , juntamente com o
constante de acoplamento entre o estado de valncia e dois estados de Rydberg. A m de estudar
a gua, desenvolvemos uma nova abordagem terica para descrever molculas triatmicas
atravs do formalismo de propagao de pacote de ondas, que reproduz com grande preciso a
estrutura vibracional os espectros experimentais RIXS de alta resoluo, permitindo obter importantes
concluses. Ns demonstramos que, devido ao acoplamento dos modos vibracionais
e anarmonicidade do potencial no estado fundamental e das superfcies de energia potencial
do estados excitados, diferentes estados excitados de camada interna em RIXS podem ser
usados como portas para sondar diferentes dinmicas de vibrao e para mapear o potencial
do estado fundamental usando modos normais de vibrao molecular. O ajuste dos raios-X
acima da ressonncia de absoro permite extrair informaes adicionais sobre o potencial do
estado fundamental, devido alta excitao vibracional. Substituio isotpica investigada por
meio de simulaes tericas e as importantes caractersticas da dinmica nuclear so discutidas,
especialmente para o estado excitado de camada interna dissociativo, onde um chamado
pico \atmico " formado. Este recurso crucial para explicar a dinmica nuclear em RIXS
da gua. Mostramos o forte potencial de experimentos RIXS de alta resoluo combinados
IV
com simulaes tericas de alto nvel para estudos avanados de estados moleculares altamente
excitados, bem como superfcies de energia potencial do estado fundamental, send utilizada
como uma tcnica auxiliar para espectroscopia ptica e infra vermelho. / This Thesis is devoted to theoretical and experimental studies of resonant inelastic X-ray
scattering (RIXS) of gas-phase carbon monoxide and water molecules. Using state-of-the-art
ab initio electronic structure calculations and a time-dependent wave packet formalism, we
make a complete analysis of the experimental RIXS spectra of the two molecular systems.
In the CO RIXS analysis, we are able to reproduce the RIXS experiment with an excellent
accuracy, allowing for a complete description of all experimental features. Interference
between di erent RIXS channels corresponding to the scattering via orthogonal molecular
orbitals in the core-excited state of CO is described. With the help of the high-resolution
spectrum and extensive ab initio simulations we show the complete breakdown of the Born-
Oppenheimer approximation in the region where forbidden nal Rydberg states are mixed
with a valence allowed nal state. Here we explain the formation of a spectral feature which
was attributed to a single state in previous studies. Moreover, through an experimentaltheoretical
combination, we improve the minimum of the valence E 1 excited state, along
with the coupling constant between the valence and two Rydberg states. In order to study
the water system, we developed a new theoretical approach to describe triatomic molecules
through the wave packet propagation formalism, which reproduces with high accuracy the
vibrational structure of the high-resolution experimental quasi-elastic RIXS spectra, allowing
to draw several important conclusions. We demonstrate that due to the vibrational
mode coupling and anharmonicity of the ground and core-excited potential energy surfaces,
di erent core-excited states in RIXS can be used as gates to probe di erent vibrational
dynamics and to map the ground state potential using molecular vibrational normal modes.
Tuning the X-rays above the absorption resonance allows to extract additional information
about the ground state potential, due to high vibrational excitation. Isotopic substitution
is investigated by theoretical simulations and important dynamical features are discussed,
especially for the dissociative core-excited state, where a so-called \atomic" peak is formed.
This feature is crucial to explain the nuclear dynamics in RIXS from water. We show the
strong potential of high-resolution RIXS experiments combined with high-level theoretical
simulations for advanced studies of highly excited molecular states, as well as of ground
state potential energy surfaces, as an auxiliary technique to optical and IR spectroscopy.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.bc.ufg.br:tede/7510 |
| Date | 08 June 2016 |
| Creators | Couto, Rafael Carvalho |
| Contributors | Guimarães, Freddy Fernandes, Guimarães, Freddy Fernandes, Norman, Patrick, Kimberg, Victor |
| Publisher | Universidade Federal de Goiás, Programa de Pós-graduação em Química (IQ), UFG, Brasil, Instituto de Química - IQ (RG) |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da UFG, instname:Universidade Federal de Goiás, instacron:UFG |
| Rights | http://creativecommons.org/licenses/by-nc-nd/4.0/, info:eu-repo/semantics/openAccess |
| Relation | Embargada polo autor/orientador em 17/06/2016. Autorizado o povoamento pelo autor/orientador em 22/06/2017., 663693921325415158, 600, 600, 600, 7826066743741197278, 1571700325303117195 |
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