A study of the self reaction of CH2ClO2 and CHCl2O2 radicals at 298 K

A low-pressure discharge-flow system equipped with laser-induced fluorescen ce (LIF) detection of NO2 and resonance-fluorescence detection of OH has be en employed to study the self reactions CH2ClO2 + CH2ClO2 --> products (1) and CHCl2O2 + CHCl2O2 --> products (2), at T = 298 K and P = 1-3 Torr. Poss ible secondary reactions involving alkoxy radicals are identified. We repor t the phenomenological rate constants (k(obs)) k(1obs) = (4.1 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1) k(2obs) = (8.6 /- 0.2) x 10(-12) cm(3) molecule(-1) s(-1) and the rate constants derived from modelling the decay profiles for both p eroxy radical systems, which takes into account the proposed secondary chem istry involving alkoxy radicals k(1) = (3.3 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1) k(2) = (7.0 +/- 1.8 ) x 10(-12) cm(3) molecule(-1) s(-1) A possible mechanism for these self reactions is proposed and QRRK calculat ions are performed for reactions (1), (2) and the self-reaction of CH3O2, C H3O2 + CH3O2 --> products (3). These calculations, although only semiquanti tative, go some way to explaining why both k(1) and k(2) are a factor of te n larger than k(3) and why, as suggested by the products of reaction (1) an d (2), it seems that the favored reaction pathway is different from that fo llowed by reaction (3). The atmospheric fate of the chlorinated peroxy spec ies, and hence the impact of their precursors (CH3Cl and CH2Cl2), in the tr oposphere are briefly discussed. HC(O)Cl is identified as a potentially imp ortant reservoir species produced from the photooxidation of these precurso rs. (C) 1999 John Wiley & Sons, Inc.