FTIR spectroscopic study of the Cl- and Br-atom initiated oxidation of ethene

Abstract

The reaction mechanism of the halogen (Cl and Br)-atom initiated oxidation of C2H4 was studied using the long path FTIR spectroscopic method in 700 torr of air at 296 ± 2 K. Among the major halogen-containing products were XCH2CHO, XCH2CH2OH, and XCH2CH2OOH (X = Cl or Br) which were shown to be formed via the self-reaction of the XCH2CH2OO radicals, i.e., 2XCH2CH2OO 2XCH2CH2O + O2; (a) 2XCH2CH2OO XCH2CHO + XCH2CH2OH + O2 and (b) followed by XCH2CH2O + O2 XCH2CHO + HO2 and XCH2CH2OO + HO2 XCH2CH2OOH + O2. From the observed yields of XCH2CHO and XCH2CH2OH the branching ratios for reactions (a) and (b) were determined to be ka/kb = 1.35 ± 0.07(2σ) for both X = Cl and Br. In addition, the O2-dependence of the rate constant for the Br + C2H4 reaction was determined by the relative rate technique as a function of O2 partial pressure from 140 to 700 torr at 700 torr total pressure of N2/O2 diluent. Rate constants for the reactions of Cl-atoms with Cl-CH2CHO and Br-atoms with Br-CH2CHO were also determined to be [4.3 ± 0.2(2sigma;)] × 10−11 and less than or equal to [1.83 ± 0.11(2σ)] × 10−13 cm3 molecule−1 s−1, respectively.