Thermal stability of carbonyl radicals. Part II. Reactions of methylglyoxyl and methylglyoxylperoxy radicals at 1 bar in the temperature range 275-311 K.
Reactions of methylglyoxyl and methylglyoxylperoxy radicals were investigated at a total pressure of 1 bar in oxygen. Methylglyoxyl radicals were generated by stationary photolysis of Br2-CH3C(O)C(O)H-NO2-O2-N2 mixtures at wavelengths > or =480 nm and of Cl2-CH3C(O)C(O)H-NO2-O2-N2 mixtures in the wavelength range 315-460 nm. In the bromine system, rate constant ratios for the reactions CH3C(O)CO --> CH3CO + CO (kdis) and CH3C(O)CO + O2 --> CH3C(O)C(O)O2 (kO2) were measured as a function of temperature in the range 275-311 K. Assuming the constant value kO2 = 5.1 x 10(-12) cm3 molecule(-1) s(-1) for our reaction conditions, kdis = 1.2 x 10(10.0+/-0.7) x exp(-11.7 +/- 3.8 kJ mol(-1)/RT) s(-1) (2sigma errors) was obtained for ptot = 1 bar (M = O2), in good agreement with the kinetic parameters calculated by Méreau et al. [R. Méreau, M.-T. Rayez, J.-C. Rayez, F. Caralp and R. Lesclaux, Phys. Chem. Chem. Phys., 2001, 3, 4712]. CH3C(O)C(O)O2 radicals oxidise NO2, forming NO3, CH3CO and CO2. This experimental result is supported by DFT and ab initio calculations. Possible mechanisms for the observed formation of several % of ketene and bromoacetyl peroxynitrate are discussed. Use of Cl rather than Br atoms to abstract the aldehydic H atom from methylglyoxal leads to chemically activated CH3C(O)CO radicals, thus substantially increasing the fraction of CH3C(O)CO radicals that decompose rather than add O2.
Jagiella
Stefan
S
Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany.
Zabel
Friedhelm
F
D002244:Carbon / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods; D005609:Free Radicals; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry; D016011:Normal Distribution; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D011312:Pressure; D011789:Quantum Theory; D013696:Temperature
D005609:Free Radicals; D009566:Nitrates; D002244:Carbon; D010100:Oxygen