| Abstract |
In the present PhD thesis, the kinetic parameters and the mechanism for the reactions of OH radicals and Cl atoms with a series of fluorinated alcohols (HFA), in the gas phase, were determined and further the tropospheric degradation of HFA was investigated. International agreements, which claim to diminish the emissions of volatile pollutants that destroy the ozone-layer (Montreal Protocol, 1987) and enhance the global warming (Kyoto Protocol, 2005), have recently proposed HFA as potential CFC alternatives. In particular, HFA are ordained to substitute HFC in a great variety of industrial and technological applications, among which the most important is their use in various refrigerating systems. However, since HFA contain CF bonds they are expected to absorb strongly in the socalled atmospheric window (800 1200 nm) and trapping the InfraRed portion of radiation, during their resident time in the troposphere, to intensify the global warming. Therefore, the most crucial property of HFA in order to elucidate their impact to the environment and climate in general, apart from IR cross section, is the tropospheric lifetime necessitating the kinetic and mechanistic study of their reactions with the atmospheric oxidants. The absolute rate coefficients for the reactions of HFA with OH radicals and Cl atoms were measured employing two different aparatus, both using the continuous flow technique of Very Low Pressure Reactor (VLPR). The ingenuity of the experimental setup is the successful coupling of Quadrupole Mass Spectrometry (QMS), which is used for qualitative and quantitative Cl atoms and stable reactants and products detection and Laser Induced Fluorescnce (LIF), which is used for OH radicals detection. The coupling of those two complimentary detection techniques equips VLPR system with the advantage to study the kinetics of Clatom and OH'radical reactions along with the capability of investigating the primary reaction mechanism and the secondary oxidation product. The results of this work showed that both Clatom and OH'radical reactions occur via the neighboring to -OH group hydrogen atom metathesis leading to HX (X: Cl, OH) and the corresponding dehydrogenated radicals. Performing oxidation experiments of the primary radicals, fluoro-carbonyl compounds were detected as the mere oxidation products consolidating the proposed mechanism as the main tropospheric dgradation pathway of HFA. The thermochemical investigation of the reaction systems via quantum mechanical molecular calculations was in excellent agreemnt with experimental results indicating that the OH group activates the adjacent hydrogen atoms weakening the C−H bond energy. Finally, both experimental and theoretical results suggest the direct interrelation between the degree and position of fluorination wit the HFAs chemical reactivity.
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Κινητική μελέτη αντιδράσεων ριζών OH και ατόμων CL με σειρά φθοριωμένων αλκοολών, στην αέρια φάση και διερεύνηση του μηχανισμού τροποσφαιρικής αποικοδόμησής τους
