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Identifier 000447091
Title Ατμοσφαιρική χημεία σειράς φθοριωμένων ολεφινών, CHF=CFX (X: H, F) : κινητική, k(T,P), και μηχανιστική διερεύνηση της αντίδρασής τους με ρίζες OH και άτομα Cl
Alternative Title Atmospheric chemistry of a series of fluorinated olefins, CHF=CFX (X: H, F): kinetic, k(T,P), and mechanistic study of their reactions with OH radicals and Cl atoms
Author Σπανουδάκη, Μαρία-Αρετή Ι.
Thesis advisor Άγγλος, Δημήτριος
Reviewer Παπαδημητρίου, Βασίλειος
Κανακίδου, Μαρία
Abstract In this MSc work, the rate coefficients for the reactions of Cl atoms and OH radicals with trifluoroethylene, (HFO-1123) (1), and the (E)- and (Z)-isomers of 1,2-difluoroethylene (HFO1132(E)/(Z)) (2), (3) and (5), (6), were measured, in the gas phase, as a function of temperature, 223 – 363 K and pressure, 30 – 700 Torr, employing the Thermostated PhotoChemical Reaction technique (TPCR/FTIR) and relative rate methods (RR). The endoxidation products for the atmospheric degradation of the three HFO were also identified using infrared spectroscopy and the product-yields were measured, where possible. HFO are the most recently proposed hydrofluorocarbons (HFC) alternatives and the first generation of substitutes that contain unsaturated bonds in their molecule, so as to ensure their high chemical reactivity. The experimental results were combined with quantum-mechanical molecular calculations in an attempt to further investigate the impact of the degree and positioning of fluorination on hydrofluoroethylenes (the simplest HFO series, C2-HFO) reactivity. The physical interpretation of the observed behaviour was also explored. The kinetic measurements revealed that the rate coefficients, k(T,P), of the studied reactions, exhibit a negative temperature dependence (Ea < 0), while the corresponding ones for the Cl atom reactions appeared to be also pressure dependent. The latter observations are consistent with electrophilic association mechanism that proceeds via a rovibrationally excited intermediate adduct. Cl kinetics experimental results were very well represented by Troe expression that models complex reactions proceeding via an intermediate adduct formation. From Troe’s expression, the fall-off parameters, at the zero- and infinite-pressure limits were obtained, using the NASA/JPL data evaluation panel recommendation for the collision broadening factor, Fc = 0.6. As far as the kinetics of OH radicals with the two isomers are concerned, the reaction rate coefficients are well represented with Arrhenius expressions. Regarding the end-oxidation products, the following ones were identified for each reaction: monofluoroformaldehyde (HC(O)F) and fluoroformaldehyde (FC(O)F), in reaction (1) and monofluoroformaldehyde (HC(O)F) in reactions (2)-(6). To further investigate the reactions mechanisms, key thermodynamic and kinetic parameters were calculated using Gaussian16 program suite, aiming to evaluate the intermediate adducts relative stability and the potent interconversion at CCSD(T)/AUG-ccpVDz//B3LYP/6-311++G(2df,2p) level of theory. Finally, the experimental results were used to obtain critical environmental metrics, namely the Radiative Efficiency (RE) and the Global Warming Potential (GWP), in order to assess the impact of the HFO series on air quality and climate.
Language Greek
Subject Hydrofluoroolefins (HFO)
Quantum-mechanical calculations
Reaction kinetics
Reactions mechanism
Relative rate method
Κβαντομηχανικοί υπολογισμοί
Κινητική αντιδράσεων
Μέθοδος σχετικής ταχύτητας
Μηχανισμός αντιδράσεων
Υδροφθορολεφίνες (HFO)
Issue date 2022-03-31
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses
  Type of Work--Post-graduate theses
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