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Identifier 000390515
Title Slice imaging studies of the ultraviolet photodissociation of dihalogens and halomethanes
Alternative Title Μελέτη υπεριώδους φωτοδιάσπασης δι-αλογόνων και αλογονο-μεθάνιου με την χρήση ιοντικής απεικόνισης τομής
Author Καρτακούλλης, Ανδρέας Ι.
Thesis advisor Κιτσόπουλος, Θεοφάνης
Reviewer Φαράντος, Σταύρος
Αναστασιάδης, Σπύρος
Ρακιτζής, Θεόδωρος-Πέτρος
Άγγλος, Δημήτριος
Κουτσολέλος, Αθανάσιος
Βελεγράκης, Μιχάλης
Abstract Understanding photochemistry at the molecular level in the bulk requires an answer to the question: How does photodissociation change with solvation from the individual molecule to the corresponding bulk? Ion imaging of the photodissociation of clusters is a viable approach to tackle this problem, Xe as the rare gas atom serves as an archetype of chemically non-reactive solvent. Slice imaging data are demonstrating the influence of clustering on the photodissociation dynamics of a diatomic molecule. ICl was dissociated at 235nm in He and Xe seed gasses, probing both Cl and I photofragment energy and angular distributions. We observe that the kinetic energy releases of both Cl and I fragments change from He to Xe seeding. For Cl fragments, the seeding in Xe increases the kinetic energy release of some Cl fragments with a narrow kinetic energy distribution, and leads to some fragments with rather broad statistical distribution falling off exponentially from near-zero energies up to about 2.5eV. Iodine fragment distribution changes even more dramatically from He to Xe seeding: sharp features essentially disappear and a broad distribution arises reaching to about 2.5eV. Both these observations are rationalized by a simple qualitative cluster model assuming ICl dissociation inside larger xenon clusters and on-surface of smaller Xe species. This thesis introduces the state-resolved dynamics of CH3I when clustered in a supersonic expansion using He and Xe as seeding gases. Following excitation at 193nm, state specific alterations in photodissociation dynamics are observed. Four vibrational levels of the CH3 umbrella vibrational mode were probed, as were Ι and Ι* atomic photofragments. For nascent CH3 fragments the measured kinetic energy releases and angular distributions show enormous sensitivity to the clustering. Manifestation of the clustering dynamics include: (a) shifting to higher energies and significant broadening of the kinetic energy distribution; (b) vibrational dependence of this increase in product kinetic energy; (c) angular distribution changes from a characteristic perpendicular character observed in free-standing CH3I into a parallel transition for the clustered moiety. Drastic effects of clustering are also observed when probing iodine-atom photofragments, namely the state resolved distribution observed when seeding in He is replaced by a broad structureless distribution when seeding in Xe.
Language English
Subject Ion imaging
Molecular clusters
Molecular reaction dynamics
Slice imaging
Ultraviolet photodissociation
Velocity map imaging
Απεικονιστική φασματοσκοπία μάζας
Ιοντικής απεικόνισης τομής
Μοριακά συσσωματώματα
Μοριακή δυναμική αντιδράσεων
Υπεριώδης φωτοδιάσπαση
Χηµική δυναµική
Issue date 2015-04-22
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
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