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| Dissertation / PhD Thesis | PUBDB-2024-05347 |
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2024
University of Oxford
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Please use a persistent id in citations: doi:10.5287/ORA-Z6JGMXRRA doi:10.3204/PUBDB-2024-05347
Abstract: This thesis uses Coulomb explosion imaging and covariance analysis to characterise concurrent fragmentation processes generating identical sets of products via different reaction pathways, highlighting the potential of extending these methods to study the photochemistry of larger, more chemically relevant species than those that have previously been studied. The photodissociation dynamics of CH2I2 at 202.5 nm were investigated using site-selective ionisation at the I 4d orbitals using photons of 95 eV. A concerted three-body dissociation process was assigned using charge transfer features and time-dependent covariance. Dynamic changes to the C-I internuclear distances and I-C-I bond angle were characterised, demonstrating the potential of Coulomb explosion imaging to simultaneously map potential energy surfaces of reaction dynamics along multiple degrees of freedom. Site-selective ionisation of 1- and 2-iodopropane at the I 4d orbitals was carried out using photons of 95 eV. Modified three-dimensional momentum covariance analysis techniques were used to disentangle fragmentation processes generating the same sets of products as well as the individual steps of multi-step fragmentation mechanisms. Observable isomeric differences demonstrated the sensitivity of individual fragmentation processes, and the corresponding nuclear dynamics, to the geometry and charge distribution of the parent polycation species. Iodobenzene was site-selectively ionised at the I 4d orbitals using photons of 120 eV, and valence-shell ionisation was also conducted using 800 nm laser pulses. Covariance analysis techniques were employed to analyse the range of products generated from stable and metastable phenyl cations and polycations, demonstrating how concurrent fragmentation processes generating long-lived species in lowly-charged cationic states can be characterised. Valence-shell ionisation could initially ionise more atomic sites than just iodine, leading to fragmentation channels that were not observed with site-selective, inner-shell ionisation. Both ionisation regimes generated similar sets of products but on different relative timescales due to initially populating different electronic excited states. Each ionisation regime results in many observable fragmentation processes, but photoelectron information is required to relate specific fragmentation channels to specific ionisation and charge generation/redistribution processes.
Keyword(s): Chemistry, Physical and theoretical
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