Kinetics of the brominated alkyl radical (CHBr2, CH3CHBr) reactions with NO2 in the temperature range 250–480 K

Abstract

The gas-phase kinetics of CHBr₂ + NO₂ and CH₃CHBr + NO₂ reactions have been studied in direct time resolved measurements using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals were generated by pulsed laser photolysis of bromoform and 1,1-dibromoethane at 248 nm. The subsequent decays of the radical concentrations were monitored as a function of [NO₂] under pseudo–first-order conditions. The rate coefficients of both reactions are independent of bath gas (He) pressure and display negative temperature dependence under the conditions of 2–6 Torr pressure (He) and 250–480 K. The obtained bimolecular rate coefficients are k(CHBr₂ + NO₂) = (9.8 ± 0.4) × 10⁻¹² (T/300 K)^{−1.65 ± 0.18} cm³ s⁻¹ (288–483 K) and k(CH₃CHBr + NO₂) = (2.27 ± 0.06) × 10⁻¹¹ (T/300 K)^{−1.28 ± 0.11} cm³ s⁻¹ (250–483 K), with the uncertainties given as one standard error. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±25%. The reaction products identified were CBr₂O for the CHBr₂ + NO₂ reaction and CHBrO and CH₃CHO with minor amounts of CH₃ for the CH₃CHBr + NO₂ reaction, respectively. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 1–11, 2012