Browsing by Author "Pekkanen, Timo Theodor"

The oxygen reactions of hydrocarbon radicals are important both in combustion and atmospheric chemistry. In this thesis I have studied the oxygen reactions of propagyl-type radicals (propargyl, 1-methylpropargyl, 3-methylpropargyl and 3-ethylpropargyl). Propargyl radical (2-propyn-1-yl) is an alkyl radical with the structure H3C≡C–CH2● . Because these radicals are resonance stabilised, their oxygen reactions are relatively slow. This means that in a combustion environment they might reach an high enough concentration for their self-reactions to become important. The self-reactions of unsaturated radicals are the first step in the formation of polyaromatic hydrocarbons. I measured the rate coefficients and equilibrium constants for the oxygen reactions of 3-methylpropargly and 3-ethylpropargly at low pressures (0.2 – 3 Torr) using a tubular flow reactor coupled to a resonance-gas-discharge-lamp photoionisation mass spectrometer (PIMS). Laser photolysis was used to generate the radicals. I have compared my experimental results to previous studies done for the propargyl + O2 and 1-methylpropargyl + O2 reactions. I reanalysed the equilibrium data from these previous studies with an improved kinetic mechanism. At temperatures below 500 K the reactions were found to be dependent on bath gas pressure and they also had negative temperature dependence. The reactivity order was found to be 3-ethylpropargyl > 3-methylpropargyl ≈ 1-methylpropargyl > propargyl. Standard reaction enthalpies and entropies are reported for all four reactions. The experimental results were combined with quantum chemical computations.