Kinetics of the reactions of Cl(²PJ) and Br(²P3/2) with O₃

A laser flash photolysis‐resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reactions Cl( 2 P J ) + O 3 → ClO + O 2 and Br( 2 P 3/2 ) + O 3 → BrO + O 2 as a function of temperature. The temperature dependence observed for the Cl( 2 P J ) + O 3 reaction is nonArrhenius, but can be adequately described by the following two Arrhenius expressions (units are cm 3 molecule −1 s −1 , errors are 2σ and represent precision only): 𝓀 1 ( T ) = (1.19 ± 0.21) × 10 −11 exp [(−33 ± 37)/ T ] for T = 189–269K and 𝓀 1 ( T ) = (2.49 ± 0.38) × 10 −11 exp[(−233 ± 46)/ T ] for T = 269–385 K. At temperatures below 230 K, the rate coefficients determined in this study are faster than any reported previously. Incorporation of our values for 𝓀 1 ( T ) into stratospheric models would increase calculated ClO levels and decrease calculated HCl levels; hence the calculated efficiency of ClO x catalyzed ozone destruction would increase. The temperature dependence observed for the ( 2 P 3/2 ) + O 3 reaction is adequately described by the following Arrhenius expression (units are cm 3 molecule −1 s −1 , errors are 2σ and represent precision only): 𝓀 2 ( T ) = (1.50 ± 0.16) × 10 −1 exp[(−775 ± 30)/ T ] for T = 195–392 K. While not in quantitative agreement with Arrhenius parameters reported in most previous studies, our results almost exactly reproduce the average of all earlier studies and, therefore, will not affect the choice of 𝓀 2 ( T ) for use in modeling stratospheric BrO x chemistry.