| Abstract
| - The mechanism of the gas-phase reaction of OH radicals with hydroxyacetone (CH3C(O)CH2OH) was studiedat 200 Torr over the temperature range 236−298 K in a turbulent flow reactor coupled to a chemical ionizationmass-spectrometer. The product yields and kinetics were measured in the presence of O2 to simulate theatmospheric conditions. The major stable product at all temperatures is methylglyoxal. However, its yielddecreases from 82% at 298 K to 49% at 236 K. Conversely, the yields of formic and acetic acids increasefrom about 8% to about 20%. Other observed products were formaldehyde, CO2 and peroxy radicals HO2and CH3C(O)O2. A partial re-formation of OH radicals (by ∼10% at 298 K) was found in the OH +hydroxyacetone + O2 chemical system along with a noticeable inverse secondary kinetic isotope effect (kOH/kOD = 0.78 ± 0.10 at 298 K). The observed product yields are explained by the increasing role of the complexformed between the primary radical CH3C(O)CHOH and O2 at low temperature. The rate constant of thereaction CH3C(O)CHOH + O2 → CH3C(O)CHO + HO2 at 298 K, (3.0 ± 0.6) × 10-12 cm3 molecule-1 s-1,was estimated by computer simulation of the concentration−time profiles of the CH3C(O)CHO product. Thedetailed mechanism of the OH-initiated oxidation of hydroxyacetone can help to better describe the atmosphericoxidation of isoprene, in particular, in the upper troposphere.
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