NASA - National Aeronautics and Space Administration

Flash photolysis-resonance fluorescence techniques were used to measure the rate constant for the reaction of OH radicals with methyl pivalate, (CH₃)₃CC(O)OCH₃ over the temperature range 250-370 K. The rate constant exhibited a weak temperature dependence, increasing at both low and high temperature from a minimum value of approximately 1.2×10^-12 cm³molecule^-1s^-1 near room temperature. The UV absorption spectrum of methyl pivalate was measured between 160 and 500 nm at room temperature. Smog chamber/ FTIR techniques were used to study the Cl atom and OH radical initiated oxidation of (CH₃)₃CC(O)OCH₃ in the presence of NOx in 700 Torr of N₂/O₂ diluent at 296 K. Relative rate techniques were used to measure k(Cl+(CH₃)₃CC(O)OCH₃) = (4.1 ± 0.5)×10^-11, k(Cl+(CH₃)₃CC(O)OCH₂Cl) = (1.8 ± 0.3)×10^-11, and k(Cl+(CH₃)₃CC(O)OC(O)OH) = (1.7 ± 0.2)×10^-11 cm³molecule^-1s^-1. The reaction of Cl atoms with (CH₃)₃CC(O)OCH₃ was found to proceed (11 ± 3) % via H-abstraction at the -OCH₃ site. The Cl atom initiated oxidation of (CH₃)₃CC(O)OCH₃ in the presence of 15-600 Torr of O₂ and 10-30 mTorr of NO_x in 700 Torr total pressure of N₂ diluent at 296 K gives HCHO, CO, acetone, CO₂, and CH₃OC(O)O₂NO₂ products. OH radical initiated oxidation of (CH₃)₃CC(O)OCH₃ in air produces acetone in a yield of 51 ± 6%. Environmental chamber experiments were performed to quantify the effect of methyl pivalate on ozone formation under simulated atmospheric conditions. An expression representing the atmospheric oxidation mechanism of methyl pivalate in computer models of atmospheric chemistry is recommended.