REACTIONS OF CH3C(O)O2 RADICALS WITH CH3O2 AND HO2 BETWEEN 263 AND 333-K - A PRODUCT STUDY

Biacetyl (butane-2,3-dione) CH3C(O)C(O)CH3 has been photolysed (lambda = 390-470 nm) at atmospheric pressure in Ar : O2 = 80 : 20 (mol/mol) mixtures between 263 and 333 K under steady-state conditions. Reaction products were analysed by matrix-isolation FTIR spectroscopy combined with a molecular-beam sampling technique. Observed reaction products were CO2, CO, HCHO, HCOOH, CH3C(O)OH, CH3C(O)OOH, CH3OH H2O2 and O3. Based on an assumed mechanism for the reaction, quantitative product data were used to determine the temperature dependence of the branching ratios beta10 and beta11 of the following two sets of CH3C(O)O2 radical reactions: CH3C(O)O2 + HO2 --> CH3C(O)OOH + O2 (10a) CH3C(O)O2 + HO2 --> CH3C(O)OH + O3 (10b) beta10 = k10a/k10b = 330 x exp(- 1430/T) and CH3C(O)O2 + CH3O2 --> CH3C(O)O + CH3O + O2 (11a) CH3C(O)O2 + CH3O2 --> CH3C(O)OH + HCHO + O2 (11b) beta11 = k11a/k11b = 2.2 x 10(6) exp(- 3870/T)