Studies of photoinduced molecular dynamics using ion imaging and correlation analysis
<p>Understanding the dynamics that connect the reactants and products of a chemical process is essential to be able to predict and potentially control the outcome. The aim of this thesis is to investigate the molecular dynamics of photoexcited polyatomic molecules in the gas phase. A range of...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2024
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| _version_ | 1817931227156447232 |
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| author | McManus, JW |
| author2 | Brouard, M |
| author_facet | Brouard, M McManus, JW |
| author_sort | McManus, JW |
| collection | OXFORD |
| description | <p>Understanding the dynamics that connect the reactants and products of a chemical process is essential to be able to predict and potentially control the outcome. The aim of this thesis is to investigate the molecular dynamics of photoexcited polyatomic molecules in the gas phase. A range of studies are presented that use femtosecond laser pulses to probe the motion of atoms within molecules. Product kinetic energy and angular distributions are recorded simultaneously using ion imaging. A photochemical process of particular interest is the rapid multiple ionisation of a molecule in an intense laser field that causes dissociation into many fragment ions, known as a Coulomb explosion. One of the main topics of this thesis is how the laser-induced Coulomb explosion of a target molecule can be used to characterising its atomic structure, including being able to track structural change following photoexcitation.</p>
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<p>Results are presented from four different experimental studies. Two of these investigated the fragmentation dynamics of molecules exposed to an intense laser field. The first is a study of the fragmentation dynamics of 1-iodopropane and 2-iodopropane polycations, prepared by site-selective ionisation of the iodine atom by an extreme-ultraviolet femtosecond laser pulse. The data analysis focuses on disentangling the competing fragmentation channels of doubly and triply charged parent ions. The second study examines the Coulomb explosion dynamics of the <em>cis</em> and <em>trans</em> isomers of 1,2-dichloroethene following strong-field ionisation by a near-infrared femtosecond laser pulse. The work explores how the parent ion charge states affects the Coulomb explosion dynamics, and hence the ability to determine structural information from the final fragment momenta.</p>
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<p>The other two experimental studies investigated the photoinduced molecular dynamics of the <em>cis</em> and <em>trans</em> isomers of 1,2-dichloroethene, excited in their (π, π<sup>∗</sup>) absorption bands using an ultrafast pump-probe scheme. The photodissociation dynamics were monitored in real time using a near-infrared laser pulse to ionise the neutral photofragments. The time-resolved momentum distribution of atomic ions produced by Coulomb explosion of highly charged <em>trans</em>-1,2-dichloroethene reveals that the molecule undergoes ultrafast structural rearrangement prior to C–Cl bond cleavage. Early attempts to model the molecular dynamics suggest that torsion about the C–C bond axis is involved.</p>
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<p>In order to establish which ions arise from the same photochemical process, experiments record all of the ions generated in each acquisition cycle and the data are processed using an analysis that measures correlation. This approach allows the fragmentation pathways of a molecule to be conclusively assigned. Taken further, it can be utilised to inspect the fragmentation dynamics of specific channels. The main correlation analysis method used in this thesis is covariance mapping. Several new techniques that expand the covariance mapping methodology are introduced and demonstrated. The other key aspect of the data analysis is the use of classical Coulomb explosion simulations to guide and support the interpretation of experimental data. Advancements in modelling the fragmentation dynamics of molecular polycations are discussed, in particular the modelling of sequential breakup mechanisms.</p> |
| first_indexed | 2024-12-09T03:18:40Z |
| format | Thesis |
| id | oxford-uuid:80b069ed-2918-4b2a-a572-ef936c9b79c4 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-12-09T03:18:40Z |
| publishDate | 2024 |
| record_format | dspace |
| spelling | oxford-uuid:80b069ed-2918-4b2a-a572-ef936c9b79c42024-10-31T10:00:31ZStudies of photoinduced molecular dynamics using ion imaging and correlation analysisThesishttp://purl.org/coar/resource_type/c_db06uuid:80b069ed-2918-4b2a-a572-ef936c9b79c4PhotodissociationFemtosecond lasersMolecular dynamicsFemtochemistryEnglishHyrax Deposit2024McManus, JWBrouard, M<p>Understanding the dynamics that connect the reactants and products of a chemical process is essential to be able to predict and potentially control the outcome. The aim of this thesis is to investigate the molecular dynamics of photoexcited polyatomic molecules in the gas phase. A range of studies are presented that use femtosecond laser pulses to probe the motion of atoms within molecules. Product kinetic energy and angular distributions are recorded simultaneously using ion imaging. A photochemical process of particular interest is the rapid multiple ionisation of a molecule in an intense laser field that causes dissociation into many fragment ions, known as a Coulomb explosion. One of the main topics of this thesis is how the laser-induced Coulomb explosion of a target molecule can be used to characterising its atomic structure, including being able to track structural change following photoexcitation.</p> <br> <p>Results are presented from four different experimental studies. Two of these investigated the fragmentation dynamics of molecules exposed to an intense laser field. The first is a study of the fragmentation dynamics of 1-iodopropane and 2-iodopropane polycations, prepared by site-selective ionisation of the iodine atom by an extreme-ultraviolet femtosecond laser pulse. The data analysis focuses on disentangling the competing fragmentation channels of doubly and triply charged parent ions. The second study examines the Coulomb explosion dynamics of the <em>cis</em> and <em>trans</em> isomers of 1,2-dichloroethene following strong-field ionisation by a near-infrared femtosecond laser pulse. The work explores how the parent ion charge states affects the Coulomb explosion dynamics, and hence the ability to determine structural information from the final fragment momenta.</p> <br> <p>The other two experimental studies investigated the photoinduced molecular dynamics of the <em>cis</em> and <em>trans</em> isomers of 1,2-dichloroethene, excited in their (π, π<sup>∗</sup>) absorption bands using an ultrafast pump-probe scheme. The photodissociation dynamics were monitored in real time using a near-infrared laser pulse to ionise the neutral photofragments. The time-resolved momentum distribution of atomic ions produced by Coulomb explosion of highly charged <em>trans</em>-1,2-dichloroethene reveals that the molecule undergoes ultrafast structural rearrangement prior to C–Cl bond cleavage. Early attempts to model the molecular dynamics suggest that torsion about the C–C bond axis is involved.</p> <br> <p>In order to establish which ions arise from the same photochemical process, experiments record all of the ions generated in each acquisition cycle and the data are processed using an analysis that measures correlation. This approach allows the fragmentation pathways of a molecule to be conclusively assigned. Taken further, it can be utilised to inspect the fragmentation dynamics of specific channels. The main correlation analysis method used in this thesis is covariance mapping. Several new techniques that expand the covariance mapping methodology are introduced and demonstrated. The other key aspect of the data analysis is the use of classical Coulomb explosion simulations to guide and support the interpretation of experimental data. Advancements in modelling the fragmentation dynamics of molecular polycations are discussed, in particular the modelling of sequential breakup mechanisms.</p> |
| spellingShingle | Photodissociation Femtosecond lasers Molecular dynamics Femtochemistry McManus, JW Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title | Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title_full | Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title_fullStr | Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title_full_unstemmed | Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title_short | Studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| title_sort | studies of photoinduced molecular dynamics using ion imaging and correlation analysis |
| topic | Photodissociation Femtosecond lasers Molecular dynamics Femtochemistry |
| work_keys_str_mv | AT mcmanusjw studiesofphotoinducedmoleculardynamicsusingionimagingandcorrelationanalysis |