DETERMINATION OF RATE CONSTANTS AND PRODUCT BRANCHING RATIOS FOR THE REACTIONS OF CH3O2 AND CH3O WITH CL ATOMS AT ROOM-TEMPERATURE

Reactions of CH3O2 and of CH3O radicals with Cl atoms have been investigated al 300 K using a discharge flow system with LIF and mass-spectrometric detection. CH3O2 + Cl --> OCl + CH3O (1a) --> HCl + CH2O2 (1b) CH3O + Cl --> HCl + HCHO (2) Rate constants k(1) = (1.15 +/- 0.3) . 10(-10) and k(2) = (1.00 +/- 0.2) . 10(-10), in units cm(3) molecule(-1) s(-1), have been obtained observing pseudo-first-order decays of CH3O2 and CHO radicals, respectively. The branching ratio k(1a)/k(1) = 0.51 +/- 0.09 has been found from the determination of OCl yields. Formation of the Criegee intermediate CH2O2 in reaction (1b) was inferred from CO2 generation. A lower limit of 0.8 +/- 0.5 was derived for the CO2 yield from unimolecular CH2O2 decomposition. Possible reaction pathways for steps (1a) and (1b) are suggested on the basis of ab initio model calculations. The calculations include the estimation of structures and energies of intermediate CH3O2Cl collision complexes and the decomposition of CH3OOCl to yield products.