Thermal Decomposition of CF₃C(O)O₂NO₂, CClF₂C(O)O₂NO₂, CCl₂FC(O)O₂NO₂, and CCl₃C(O)O₂NO₂

Abstract

Abstract Haloacetyl, peroxynitrates are intermediates in the atmospheric degradation of a number of haloethanes. In this work, thermal decomposition rate constants of CF 3 C(O)O 2 NO 2 , CClF 2 C(O)O 2 NO 2 , CCl 2 FC(O)O 2 NO 2 , and CCl 3 C(O)O 2 NO 2 have been determined in a temperature controlled 420 l reaction chamber. Peroxynitrates ( R O 2 NO 2 ) were prepared in situ by photolysis of R H/Cl 2 /O 2 /NO 2 /N 2 mixtures ( R = CF 3 CO, CClF 2 CO, CCl 2 FCO, and CCl 3 CO). Thermal decomposition was initiated by addition of NO, and relative R O 2 NO 2 concentrations were measured as a function of time by long‐path IR absorption using an FTIR spectrometer. First‐order decomposition rate constants were determined at atmospheric pressure (M = N 2 ) as a function of temperature and, in the case of CF 3 C(O)O 2 NO 2 and CCl 3 C(O)O 2 NO 2 , also as a function of total pressure. Extrapolation of the measured rate constants to the temperatures and pressures of the upper troposphere yields thermal lifetimes of several thousands of years for all of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitrates may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rates. Results on the thermal decomposition of CClF 2 CH 2 O 2 NO 2 and CCl 2 FCH 2 O 2 NO 2 are also reported, showing that the atmospheric lifetimes of these 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 CF 3 C(O)O 2 radicals with NO 2 and NO was determined to be 0.64 ± 0.13 (2σ) at 315 K and a total pressure of 1000 mbar (M = N 2 ). © 1994 John Wiley & Sons, Inc.