THERMAL-DECOMPOSITION OF CF3C(O)O2NO2, CCLF2C(O)O2NO2, CCL2FC(O)O2NO2, AND CCL3C(O)O2NO2

Haloacetyl peroxynitrates are intermediates in the atmospheric degrada tion of a number of haloethanes. In this work, thermal decomposition r ate constants of CF3C(O)O2NO2, CClF2C(O)O2NO2, CCl2FC(O)O2NO2, and CCl 3C(O)O2NO2 have been determined in a temperature controlled 420 1 reac tion chamber. Peroxynitrates (RO2NO2) were prepared in situ by photoly sis of RH/Cl2/O2/NO2/N2 mixtures (R = CF3CO, CClF2CO, CCl2FCO, and CCl 3CO). Thermal decomposition was initiated by addition of NO, and relat ive RO2NO2 concentrations were measured as a function of time by long- path IR absorption using an FTIR spectrometer. First-order decompositi on rate constants were determined at atmospheric pressure (M = N2) as a function of temperature and, in the case of CF3C(O)O2NO2 and CCl3C(O )O2NO2, also as a function of total pressure. Extrapolation of the mea sured rate constants to the temperatures and pressures of the upper tr oposphere yields thermal lifetimes of several thousands of years for a ll of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitra tes may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rate s. Results on the thermal decomposition of CClF2CH2O2NO2 and CCl2FCH2O 2NO2 are also reported, showing that the atmospheric lifetimes of thes e peroxynitrates are very short in the lower troposphere and increase to a maximum of several days close to the tropopause. The ratio of the rate constants for the reactions of CF3C(O)O2 radicals with NO2 and N O was determined to be 0.64 +/- 0.13 (2sigma) at 315 K and a total pre ssure of 1000 mbar (M = N2). (C) 1994 John Wiley & Sons, Inc.