Photoinduced chemistry of biomolecular building blocks and molecules in space
<p>The interactions between light and matter are ubiquitous in the universe and initiate many fundamental chemical processes, such as photosynthesis and vitamin D production. Therefore, gaining a better understanding of how light interacts with molecules and how light-induced reaction mechanis...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2023
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| _version_ | 1797112926293721088 |
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| author | Milesevic, D |
| author2 | Vallance, C |
| author_facet | Vallance, C Milesevic, D |
| author_sort | Milesevic, D |
| collection | OXFORD |
| description | <p>The interactions between light and matter are ubiquitous in the universe and initiate many fundamental chemical processes, such as photosynthesis and vitamin D production. Therefore, gaining a better understanding of how light interacts with molecules and how light-induced reaction mechanisms develop from reactants to products is of great interest.</p>
<p>This work uses a velocity-map imaging time-of-flight spectrometer to study the unimolecular photodissociation dynamics of molecules in the gas phase. The observables of the experiment are the product scattering distributions, which are a fingerprint of the chemical reaction, and the product time-of-flight, which reveals the fragment identities. The experiments aim to understand which chemical bonds break, how the system evolves on the potential energy surfaces involved in the reaction, and how the available energy is distributed over the product degrees of freedom.</p>
<p>The first part of this thesis studies the photodissociation of tetrahydrofuran at 193 nm, N,N-dimethylformamide at 225 nm and 245 nm, and the N,N-dimethylformamide cation at 225nm, 245nm, and 280nm. Tetrahydrofuran is a model for the DNA backbone molecule ribose, and N,N-dimethylformamide is a model for the peptide bond, which forms the backbone of proteins. Both molecules reveal complex dissociation dynamics, in which population transfer to lower electronic states is possible after the initial excitation. This population transfer probably plays an important role in the photoprotection of molecules in biological species. The great majority of the available energy is distributed into the internal product modes rather than product kinetic energy. This observation is pronounced in the N,N-dimethylformamide cation study, in which a change in photon energy of more than 0.5 eV leads to the same product kinetic energy release.</p>
<p>The second part of the thesis describes the design and characterization of a novel femtosecond laser beamline to the experiment which allows us to conduct Coulomb explosion imaging experiments, and a fibre-coupled laser-induced thermal desorption source capable of introducing non-volatile samples into the spectrometer. In a study combining both techniques, we investigate the fragmentation pattern of three singly and doubly charged polycyclic aromatic hydrocarbons: triphenylene, perylene, and benzo[a]pyrene. All three molecules display a common fragmentation pattern in which the summed number of carbon atoms in the fragment ions deviates from the carbon number of the parent molecule by a multiple of two, which we interpret in terms of a fragmentation mechanism involving sequential loss of neutral acetylene (C2H2) units. We also show that loss of the neutral acetylene units occurs preferably from the heavier fragment ion after an initial charge separation step.</p> |
| first_indexed | 2024-04-09T03:54:56Z |
| format | Thesis |
| id | oxford-uuid:85ef0667-4ec6-46c4-b1a3-8fa99fae6bd9 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-04-09T03:54:56Z |
| publishDate | 2023 |
| record_format | dspace |
| spelling | oxford-uuid:85ef0667-4ec6-46c4-b1a3-8fa99fae6bd92024-03-13T10:41:52ZPhotoinduced chemistry of biomolecular building blocks and molecules in spaceThesishttp://purl.org/coar/resource_type/c_db06uuid:85ef0667-4ec6-46c4-b1a3-8fa99fae6bd9Laser photochemistryChemistry, Physical and theoreticalIon imagingReaction dynamicsEnglishHyrax Deposit2023Milesevic, DVallance, C<p>The interactions between light and matter are ubiquitous in the universe and initiate many fundamental chemical processes, such as photosynthesis and vitamin D production. Therefore, gaining a better understanding of how light interacts with molecules and how light-induced reaction mechanisms develop from reactants to products is of great interest.</p> <p>This work uses a velocity-map imaging time-of-flight spectrometer to study the unimolecular photodissociation dynamics of molecules in the gas phase. The observables of the experiment are the product scattering distributions, which are a fingerprint of the chemical reaction, and the product time-of-flight, which reveals the fragment identities. The experiments aim to understand which chemical bonds break, how the system evolves on the potential energy surfaces involved in the reaction, and how the available energy is distributed over the product degrees of freedom.</p> <p>The first part of this thesis studies the photodissociation of tetrahydrofuran at 193 nm, N,N-dimethylformamide at 225 nm and 245 nm, and the N,N-dimethylformamide cation at 225nm, 245nm, and 280nm. Tetrahydrofuran is a model for the DNA backbone molecule ribose, and N,N-dimethylformamide is a model for the peptide bond, which forms the backbone of proteins. Both molecules reveal complex dissociation dynamics, in which population transfer to lower electronic states is possible after the initial excitation. This population transfer probably plays an important role in the photoprotection of molecules in biological species. The great majority of the available energy is distributed into the internal product modes rather than product kinetic energy. This observation is pronounced in the N,N-dimethylformamide cation study, in which a change in photon energy of more than 0.5 eV leads to the same product kinetic energy release.</p> <p>The second part of the thesis describes the design and characterization of a novel femtosecond laser beamline to the experiment which allows us to conduct Coulomb explosion imaging experiments, and a fibre-coupled laser-induced thermal desorption source capable of introducing non-volatile samples into the spectrometer. In a study combining both techniques, we investigate the fragmentation pattern of three singly and doubly charged polycyclic aromatic hydrocarbons: triphenylene, perylene, and benzo[a]pyrene. All three molecules display a common fragmentation pattern in which the summed number of carbon atoms in the fragment ions deviates from the carbon number of the parent molecule by a multiple of two, which we interpret in terms of a fragmentation mechanism involving sequential loss of neutral acetylene (C2H2) units. We also show that loss of the neutral acetylene units occurs preferably from the heavier fragment ion after an initial charge separation step.</p> |
| spellingShingle | Laser photochemistry Chemistry, Physical and theoretical Ion imaging Reaction dynamics Milesevic, D Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title | Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title_full | Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title_fullStr | Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title_full_unstemmed | Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title_short | Photoinduced chemistry of biomolecular building blocks and molecules in space |
| title_sort | photoinduced chemistry of biomolecular building blocks and molecules in space |
| topic | Laser photochemistry Chemistry, Physical and theoretical Ion imaging Reaction dynamics |
| work_keys_str_mv | AT milesevicd photoinducedchemistryofbiomolecularbuildingblocksandmoleculesinspace |