Atmospheric Chemistry of Pivalaldehyde and Isobutyraldehyde: Kinetics and Mechanisms of Reactions with Cl Atoms, Fate of (CH_3)_3CC(O) and (CH_3)_2CHC(O) Radicals, and Self-Reaction Kinetics of (CH_3)_3CC(O)O_2 and (CH_3)_2CHC(O)O_2 Radicals

摘要

The kinetics and mechanism of the reactions Cl + (CH_3)_3CCHO and Cl + (CH_3)_2CHCHO were investigated at room temperature using two complementary techniques: flash photolysis/UV absorption and continuous photolysis/Fourier transform infrared (FTIR) smog chamber. Reactions proceed predominantly by abstraction of the aldehydic H atom to form acyl radicals. FTIR measurements indicated that the acyl-forming channel accounts for 81% ± 8% and 85% ± 10% of the reaction of Cl atoms with (CH_3)_3CCHO and (CH_3)_2CHCHO. UV measurements indicated that the acyl-forming channel accounts for 88% ± 6% and 85% ± 5% of the reaction of Cl atoms with (CH_3)_3CCHO and (CH_3)_2CHCHO. The atmospheric fate (>98%) of the resulting (CH_3)_3CC(O) and (CH_3)_2CHC(O) radicals is an addition of O_2 to give the corresponding acylperoxy radical. In 700 Torr of N_2/O_2 mixtures at a temperature of 296 K, the decomposition of (CH_3)_3CC(O) and (CH_3)_2CHC(O) radicals via CO elimination occurs at rates of ～1 * 10~5 and ～4 * 10~3 s~(-1), respectively. Relative rate methods were used to measure the reaction rates (in units of cm~3 molecule~(-1) s~(-1)): k(Cl + (CH_3)_3CCHO) = (1.15 ± 0.30) * 10~(-10); k(Cl + (CH_3)_2CHCHO) = (1.33 ± 0.25) * 10~(-10); k(Cl + (CH_3)_3CC(O)Cl) = (6.86 ± 1.50) * 10~(-12); k(Cl + (CH_3)_2CHC(O)Cl) = (7.82 ± 2.10) * 10~(-12); k(Cl + (CH_3)_3CCl) = (1.27 ± 0.21) * 10~(-11); and k(Cl + (CH_3)_2CHCCl) = (2.01 ± 0.49) * 10~*(-11). Self-reaction rate constants were measured for (CH_3)_3CC(O)O_2 and (CH_3)_2CHC(O)O_2 radicals and compared to previous measurements.