No abstract

A low-pressure discharge-flow system equipped with laser-induced fluorescence (LIF) detection of NO 2 and resonance-fluorescence detection of OH has been employed to study the self reactions CH 2 ClO 2 ϩ CH 2 ClO 2 : products (1) and CHCl 2 O 2 ϩ CHCl 2 O 2 : products (2), at T ϭ 298 K and P ϭ 1-3 Torr. Possible secondary reactions involving alkoxy radicals are identified. We report the phenomenological rate constants (k obs ) k 1obs ϭ (4.1 Ϯ 0.2) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 k 2obs ϭ (8.6 Ϯ 0.2) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 and the rate constants derived from modelling the decay profiles for both peroxy radical systems, which takes into account the proposed secondary chemistry involving alkoxy radicals k 1 ϭ (3.3 Ϯ 0.7) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 k 2 ϭ (7.0 Ϯ 1.8) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 A possible mechanism for these self reactions is proposed and QRRK calculations are performed for reactions (1), (2) and the self-reaction of CH 3 O 2 , CH 3 O 2 ϩ CH 3 O 2 : products (3). These calculations, although only semiquantitative, go some way to explaining why both k 1 and k 2 are a factor of ten larger than k 3 and why, as suggested by the products of reaction (1) and (2), it seems that the favored reaction pathway is different from that followed by reaction (3). The atmospheric fate of the chlorinated peroxy species, and hence the impact of their precursors (CH 3 Cl and CH 2 Cl 2 ), in the troposphere are briefly discussed. HC(O)Cl is identified as a potentially important reservoir species produced from the photooxidation of these precursors.