ABSTRACT
Glycolaldehyde, HOCH2CHO, is an important multifunctional atmospheric trace gas formed in the oxidation of ethylene and isoprene and emitted directly from burning biomass. The initial step in the atmospheric photooxidation of HOCH2CHO yields HOCH2CO and HOCHCHO radicals; both of these radicals react rapidly with O2 in the troposphere. This study presents a comprehensive theoretical investigation of the HOCH2CO + O2 and HOCHCHO + O2 reactions using high-level quantum chemical calculations and energy-grained master equation simulations. The HOCH2CO + O2 reaction results in the formation of a HOCH2C(O)O2 radical, while the HOCHCHO + O2 reaction yields (HCO)2 + HO2. Density functional theory calculations have identified two open unimolecular pathways associated with the HOCH2C(O)O2 radical that yield HCOCOOH + OH or HCHO + CO2 + OH products; the former novel bimolecular product pathway has not been previously reported in the literature. Master equation simulations based on the potential energy surface calculated here for the HOCH2CO + O2 recombination reaction support experimental product yield data from the literature and indicate that, even at total pressures of 1 atm, the HOCH2CO + O2 reaction yields â¼11% OH at 298 K.
ABSTRACT
The dissociation of 2-methyl furan at high temperatures has been studied in a combined experimental and theoretical approach to elucidate the details of this multi-channel unimolecular reaction. Laser schlieren densitometry studies were performed in a diaphragmless shock tube over the range 1600 < T < 2300 K and three pressures 60, 120 and 240 Torr. The theoretical study identified many reaction paths, most of which are initiated by the formation of carbenes. Of these paths, five account for 99% consumption of 2MF, and three account for 95% consumption. Simulations of the experimental results with a model that incorporated the theoretical predictions of reaction paths failed to reproduce the experimental data. This was resolved by increasing the rate of loss of an H-atom from the methyl group in 2-methyl furan by a factor of 2-4. The resulting model provides good simulations of the complete set of experimental data. The branching fractions for the three key reactions are both temperature and pressure dependent.
