101 |
Pressure Effects on Electric Field Spectra of Molecular Rydberg StatesAltenloh, Daniel Dean 12 1900 (has links)
Electric field studies, electrochromism, were used to obtain excited-state data for analogous divalent sulfur compounds. The sulfides investigated were dimethyl sulfide and small cyclic sulfides including the three to six member ring compounds. The excited-state dipole moments and polarizabilities are reported for the first s, p, and d Rydberg absorption bands which occur in the near vacuum ultraviolet region from 230 to 170 nm. The excited-state data are interpreted in terms of the particular excited-state (s, p, or d) for the molecules and the bending differences due to the presence of the ring and the number of atoms in the ring. The next section describes the use of electrochromism to investigate the pressure effect of argon, carbon tetrafluoride and sulfur hexafluoride on the spectra for molecular Rydberg states.
|
102 |
Estudo químico-quântico da estabilidade das N-alquil nitrosaminas neutras e protonadasAndrade, Railton Barbosa de 23 February 2016 (has links)
Submitted by ANA KARLA PEREIRA RODRIGUES (anakarla_@hotmail.com) on 2017-08-01T13:42:01Z
No. of bitstreams: 1
arquivototal.pdf: 3885187 bytes, checksum: 43a97495626de95064ede3adad23bcd9 (MD5) / Made available in DSpace on 2017-08-01T13:42:01Z (GMT). No. of bitstreams: 1
arquivototal.pdf: 3885187 bytes, checksum: 43a97495626de95064ede3adad23bcd9 (MD5)
Previous issue date: 2016-02-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work we performed ωB97XD, CAM-B3LYP, CASSCF, MR-CISD, MRCISD+
Q and NEVPT2 calculations. The basis sets aug-cc-pVDZ and cc-pVTZ were used to
assess the stability of certain neutral and protonated N-nitrosamines in the ground and
excited states. In addition, we analyzed the effect of methylation on proton transfer. The
initial proposal was to characterize the stationary points and the potential energy curves in
the ground and excited state, in order to suggest a strategy that results in lower
computational demand to be applied in larger systems (cyclic and bicyclic N-nitrosamines).
The results indicate that the methodology MR-CISD/cc-pVTZ//MR-CISD/aug-cc-pVDZ
may be appropriate to study the N-nitrosamines. The used functionals provided good
descriptions to vertical excitation energy, but were not capable to represent the states
correctly to dissociation curves. MR-CID+Q/cc-pVTZ results for the system (CH3)2NNO
protonated indicate that protonation is more favorable for NDMA_1A, increasing energy in
17.5 kcal mol-1, and that the methylation significantly alter the intramolecular proton
transfer barriers. With the aim to find a methodology with lower computational cost, use a
reference wave function CASSCF (12, 9) at the level NEVPT2/cc-pVTZ was used study the
neutral NDMA and results were consistent with both the theoretical and experimental
parameters in the literature. For studies involving larger systems, for example, cyclic and
bicyclic N-nitrosamines, NEVPT2 may be used, since it is completely paralyzed, and
involves the use of a CASSCF larger than CAS (14, 10), which is a fundamental
characteristic to study larger systems. / Neste trabalho foram realizados cálculos ωB97XD, CAM-B3LYP, CASSCF, MRCISD,
MR-CISD+Q e NEVPT2. Os conjuntos de base aug-cc-pVDZ e cc-pVTZ foram
usados para avaliar a estabilidade de algumas N-nitrosaminas neutras e protonadas nos
estados fundamental e excitado. Além disso, foi analisado o efeito da metilação nas
transferências de próton. A proposta inicial foi caracterizar os pontos estacionários, as
curvas de energia potencial no estado fundamental e excitado, com a finalidade de sugerir
uma estratégia que resulte em menor demanda computacional para ser aplicada em
sistemas maiores (N-nitrosaminas cíclicas e bicíclicas). Os resultados indicaram que a
metodologia MR-CISD/cc-pVTZ//MR-CISD/aug-cc-pVDZ pode ser adequada para estudar
as N-nitrosaminas. Os funcionais utilizados forneceram boas descrições para a energia de
excitação vertical, mas para as curvas de dissociação não foram capazes de representar os
estados corretamente. Os resultados com MR-CISD+Q/cc-pVTZ para o sistema
(CH3)2NNO protonado indicam que a protonação é mais favorável para NDMA_1A,
aumentando a energia em 17,5 kcal mol-1, e que a metilação altera significativamente as
barreiras de transferência de próton intramoleculares. Com a proposta de encontrar uma
metodologia com menor custo computacional, utilizou-se uma função de onda de
referência CASSCF (12, 9) a nível NEVPT2/cc-pVTZ para estudar a NDMA neutra e os
resultados foram compatíveis com os parâmetros experimentais e teóricos existentes na
literatura. Para estudos envolvendo sistemas maiores, por exemplo, N-nitrosaminas cíclicas
e bicíclicas, NEVPT2 poderá ser usado, uma vez que está totalmente paralelizado e
comporta a utilização de um CASSCF maior que CAS (14, 10), característica fundamental
para estudar sistemas maiores.
|
103 |
Excited State Dynamics in Nanostructured Polymer Systems / 高分子ナノ構造内における励起状態ダイナミクスTamai, Yasunari 25 March 2013 (has links)
Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17595号 / 工博第3754号 / 新制||工||1572(附属図書館) / 30361 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 赤木 和夫, 教授 金谷 利治 / 学位規則第4条第1項該当
|
104 |
DEVELOPMENT AND APPLICATION OF EFFECTIVE FRAGMENT POTENTIALS FOR (BIO)MOLECULAR SYSTEMSYongbin Kim (9187811) 31 July 2020 (has links)
<div>
<div>
<div>
<p>The Effective Fragment Potential (EFP) is a quantum-mechanical based model potential for
accurate calculations of non-covalent interactions between molecules. It can be coupled with ab
initio methods in so-called QM/EFP models to explore the electronic properties of extended
molecular systems by providing rigorous description of surrounding environments. The current
EFP formulation is, however, not well suited for large-scale simulations due to its inherent
limitation of representing effective fragments as rigid structures. The process of utilizing EFP
method for the molecular systems with flexible degrees of freedom entails multiple sets of
parameter calculations requiring intensive computational resources. This work presents
development of the EFP method for describing flexible molecular systems, so-called Flexible EFP.
To validate the applicability of the Flexible EFP method, extensive benchmark studies on the
amino acid interactions, binding energies, and electronic properties of flavin chromophore of the
cryptochrome protein have been demonstrated. In addition to methodological developments,
excitonic properties of the Fenna-Matthews-Olson (FMO) photosynthetic pigment-protein
complex are explored. In biological systems where intermolecular interactions span a broad range
from non-polar to polar and ionic forces, EFP is superior to the classical force fields. In the present
study, we demonstrate excellent performance of the QM/EFP model for predicting excitonic
interactions and spectral characteristics of the FMO wildtype complex. We characterize the key
factors for accurate modeling of electronic properties of bacteriochlrophyll a (BChl a)
photosynthetic pigments and suggest a robust computational protocol that can be applied for
modeling other photosynthetic systems. Developed computational procedures were also
successfully utilized to elucidate photostability and triplet dynamics in the FMO complex and
spectroscopic effects of single-point mutagenesis in FMO. A combination of polarizable EFP
molecular dynamics and QM/EFP vibrational frequency calculations were also applied to
understanding and interpreting structures and Raman spectroscopy of tert-butyl alcohol solutions.
</p>
</div>
</div>
</div>
|
105 |
Picosecond Spectroscopy of Rhodamine BClark, James Burton 12 1900 (has links)
A series of picosecond excite-probe experiments was performed on various concentrations of aqueous and ethanolic solutions of rhodamine B in order to determine the existence of dimerization in those solutions. The goals of the research presented in this dissertation were twofold. Initially, various techniques of time-resolved spectroscopy were to be employed to further characterize the ground and excited-state molecular properties of the aqueous RB dimer. The information obtained, and the techniques developed in that study would then be utilized in an effort to secure evidence which would support or refute the claims of rhodamine B dimerization in an ethanolic solution.
|
106 |
Investigating Ultrafast Photoexcited Dynamics of Organic ChromophoresChakraborty, Pratip, 0000-0002-0248-6193 January 2020 (has links)
Light or photons can excite electrons in a molecule, leading to creation of electronically excited states. Such processes are ubiquitous in nature, such as, vision, photo-protection of DNA/RNA nucleobases, light harvesting, energy and charger transfer etc. This photoexcitation induces nuclear motion on the excited states, leading the excess energy to dissipate either non-radiatively via internal conversion back down to the ground state, isomerization, and dissociation, or radiatively via fluorescence and phosphorescence. In this dissertation, we investigate the non-radiative processes in organic chromophores that ensue in an ultrafast manner, mediated via conical intersections (CoIn). Description of such excited state processes generally require multi-reference treatment because of quasi-degeneracy near CoIns. Hence, most insight about these processes is typically gained by constructing potential energy surface (PES) using multi-reference electronic structure methods along important reaction coordinates. Nonetheless, the aforementioned static treatment fails to provide any dynamical information, such as, excited state lifetime, state populations, branching ratio, quantum yield etc. In this dissertation, we have gone beyond the static treatment by undertaking computationally expensive non-adiabatic excited state molecular dynamics simulations employing trajectory surface hopping (TSH) methodology on PESs created on-the-fly using multi-reference electronic structure methods. This allows us to compare theoretical results to experimental observables, when possible, strengthening the explanations underlying those processes.
Our goal is to examine the effect of structure, and of electronic structure methods on the excited state dynamics. We have examined the non-adiabatic excited state dynamics of cis,cis-1,3-cyclooctadiene (cc-COD), a cyclic diene, in an effort to systematically compare and contrast the dynamics of cc-COD to that of other well studied conjugated molecules. Such exploration is very significant, since the majority of the molecules involved in natural photoexcited processes, include an ethylenic double bond or alternating double bonds creating conjugation. Our calculations have revealed ultrafast sub-ps decay for cc-COD, and have illustrated that the internal conversion dynamics is facilitated by CoIns, dominated by twisting of one of the double bonds and pyramidalization of one of the carbons of that double bond, similar to trans-1,3-butadiene and unlike 1,3-cyclohexadiene (CHD). Our high-level electronic structure calculations have also explained the features in the experimental time-resolved photoelectron spectrum of cc-COD. Another molecule of biological importance, uracil, was also investigated using TSH simulations, by systematically increasing dynamical correlation. We have found that the inclusion of dynamical correlation for uracil leads to an almost barrierless PES on S2, leading to a faster decay and no population trap on this state. Uracil also contains a double bond and the simulations have revealed that the ultrafast relaxation is dominated by an ethylenic twist and pyramidalization of a carbon of that bond, increasing importance of such nuclear motion in photoexcited molecular dynamics. A comparison of the molecules studied have illustrated that the rigid molecules, such as uracil, CHD, have a very local CoIn seam space, whereas cc-COD, which is flexible having many low frequency degrees of freedom, has a non-local or extended CoIn seam space. Overall, the work performed in this dissertation, elucidates the significance of structure and conjugation, in the photoinduced coupled electron-nuclear dynamics in organic molecules. / Chemistry
|
107 |
Tuning the Excited States and Reactivity of Polypyridyl Ru(II) Complexes for PhotochemotherapyLoftus, Lauren Marie January 2019 (has links)
No description available.
|
108 |
A Study of <sup>9</sup>B Spectroscopy via the <sup>9</sup>Be(p,n)<sup>9</sup>B Reaction using the Neutron Time-of-Flight TechniqueKarki, Alina January 2013 (has links)
No description available.
|
109 |
Vibrational and Excited-State Dynamics of DNA Bases Revealed by UV and Infrared Femtosecond Time-Resolved SpectroscopyMiddleton, Chris T. 24 June 2008 (has links)
No description available.
|
110 |
Syntheses and Optoelectronic Characterizations of Thiophene Carboxylate Ligated Quadruply Bonded Dimolybdenum and Ditungsten CompoundsGhosh, Yagnaseni 27 August 2009 (has links)
No description available.
|
Page generated in 0.1679 seconds