Experimental and Theoretical Studies of Reactions of Halogenated Species of Atmospheric Interest.

This dissertation presents the results of experimental and theoretical studies of halogenated species and reactions of atmospheric interest. Ab initio calculations have been used with isogyric and isodesmic schemes to evaluate the heats of formation for species such as HCO, FCO, HFCO, HClCO, HO_2, FO and FO_2 . The calculated values have proven reliable by comparison with available experimental data. Ab initio calculations have also been used to examine the main features of the potential energy surface of complicated reaction systems. Calculations on the FCO + O_2 to FC(O)O_2 reaction system predict that this reaction is thermodynamically and kinetically the preferred pathway. This result leads to the postulation of an ozone regenerating catalytic cycle. Theoretical examinations of dissociation pathways of the HXCO (where X = F, Cl and Br) show that the molecular elimination of HX is the lowest energy pathway. The reaction F + HFCO and multiphoton dissociation of FBrCO molecule have been studied for the laboratory generation of FCO radicals. The rate coefficient for the reaction F + HFCO to HF + FCO has been determined as k (T) = (4.4 +/- 2.6) times 10 ^{-11} exp (-(1800 +/- 400/RT)) cm^3 molecule ^{-1} s^{-1 } over 298-368 K range by the IRMPD/chemiluminesence technique. FCO radicals produced are predicted theoretically to undergo rapid reaction via FCO + FCO to F_2CO + CO through a hot F_2C_2O _2. The threshold intensity for the photolysis of FBrCO by a CO_2 laser is estimated to be 143.4 +/- 15 MW cm^ {-2} and the favorable path of FBrCO dissociation is the formation of Br and FCO. The reaction system of F + CH_4 has been studied using the IRMPD/LIF technique with the aid of theoretical calculated energetics for major secondary reactions. Evidence of energy transfer for the CH radical from the B^2 Sigma^- state to the A^2 Delta state has been observed and a mechanism for the formation of the CH(A^2Delta ) state has been postulated.