Temperature-Dependent Rate Coefficient Measurements for the Reaction of Bromine Atoms with Trichloroethene, Ethene, Acetylene, and Tetrachloroethene in Air

摘要

In this artjcle, rate coefficients for the reactio~ of Br atoms with a series of un- saturated species (trichloroethene. kl; ethene, k2; acetylene. k3; and tetrachloroethene, k4) are reported in 700 Tori air over the temperature range 228-298 K. The data were obtained in a temperature-regulated environmental chamber/FrIR spectrometer system, using standard rel- ative rate techniques. with the reaction of Br with CH2O and CH3CHO as the reference reac- tions. Room-temperature values for kl through k4 were found to be 1.56 X 10-13. 1.23 X 10-13, 2.86 x 10-14, and <1.2 X 10-16 cm3 molecule-1 S-I. respectively. in reasonable accord with previously available data. At 240 K. values of kl = 1.77 x 10-12, k2 = 5.76 X to-13. k3 = 3.97 X 10-14. and k4 = 3.22 X 10-15 cm3 molecule-1 S-I are reported. These k2 and k3 values are 2-3 times lower than those currently in use. which are obtained by extrapolation of pre- vious measurements made over the range 298-350 K [Barnes etal., 1989]. An investigation of the mechanism of the Br-atom~initiated oxidation of acetylene. trichloroethene, and tet- rachloroethene 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. 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 acetvlene oxidation).k_(17) = 1.1*10~(-14)cm~3 molecule~(-1)s~(-1),is also reported. k,7 = I.1 X 10-1.4 cm3 molecJlp-1 S-I is ;llsn