Atmospheric Chemistry of Pivalaldehyde and Isobutyraldehyde: Kinetics and Mechanisms of Reactions with Cl Atoms, Fate of (CH3)3CC(O) and (CH3)2CHC(O) Radicals, and Self-Reaction Kinetics of (CH3)3CC(O)O2 and (CH3)2CHC(O)O2 Radicals

Abstract

The kinetics and mechanism of the reactions Cl + (CH3)3CCHO and Cl + (CH3)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 (CH3)3CCHO and (CH3)2CHCHO. UV measurements indicated that the acyl-forming channel accounts for 88% ± 6% and 85% ± 5% of the reaction of Cl atoms with (CH3)3CCHO and (CH3)2CHCHO. The atmospheric fate (>98%) of the resulting (CH3)3CC(O) and (CH3)2CHC(O) radicals is an addition of O2 to give the corresponding acylperoxy radical. In 700 Torr of N2/O2 mixtures at a temperature of 296 K, the decomposition of (CH3)3CC(O) and (CH3)2CHC(O) radicals via CO elimination occurs at rates of ∼1 × 105 and ∼4 × 103 s-1, respectively. Relative rate methods were used to measure the reaction rates (in units of cm3 molecule-1 s-1): k(Cl + (CH3)3CCHO) = (1.15 ± 0.30) × 10-10; k(Cl + (CH3)2CHCHO) = (1.33 ± 0.25) × 10-10; k(Cl + (CH3)3CC(O)Cl) = (6.86 ± 1.50) × 10-12; k(Cl + (CH3)2CHC(O)Cl) = (7.82 ± 2.10) × 10-12; k(Cl + (CH3)3CCl) = (1.27 ± 0.21) × 10-11; and k(Cl + (CH3)2CHCCl) = (2.01 ± 0.49) × 10-11. Self-reaction rate constants were measured for (CH3)3CC(O)O2 and (CH3)2CHC(O)O2 radicals and compared to previous measurements.