Temperature‐dependent rate coefficient measurements for the reaction of bromine atoms with trichloroethene, ethene, acetylene, and tetrachloroethene in air

In this article, rate coefficients for the reaction of Br atoms with a series of unsaturated species (trichloroethene, k 1 ; ethene, k 2 ; acetylene, k 3 ; and tetrachloroethene, k 4 ) are reported in 700 Torr air over the temperature range 228–298 K. The data were obtained in a temperature‐regulated environmental chamber/FTIR spectrometer system, using standard relative rate techniques, with the reaction of Br with CH 2 O and CH 3 CHO as the reference reactions. Room‐temperature values for k 1 through k 4 were found to be 1.56 × 10 −13 , 1.23 × 10 −13 , 2.86 × 10 −14 , and <1.2 × 10 −16 cm 3 molecule −1 s −1 , respectively, in reasonable accord with previously available data. At 240 K, values of k 1 = 1.77 × 10 −12 , k 2 = 5.76 × 10 −13 , k 3 = 3.97 × 10 −14 , and k 4 = 3.22 × 10 −15 cm 3 molecule −1 s −1 are reported. These k 2 and k 3 values are 2–3 times lower than those currently in use, which are obtained by extrapolation of previous measurements made over the range 298–350 K [Barnes et al., 1989]. An investigation of the mechanism of the Br‐atom–initiated oxidation of acetylene, trichloroethene, and tetrachloroethene was also conducted as a function of temperature. Although no temperature dependence to the product yields was observed for any of the systems studied, the product distributions were found to be altered by the presence of NO x in the case of trichloroethene and tetrachloroethene. An anomalously low rate coefficient for the reaction of Br with glyoxal (HC(O)CHO, a product of acetylene oxidation), k 17 = 1.1 × 10 −14 cm 3 molecule −1 s −1 , is also reported. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 198–211, 2001