Laser flash photolysis studies of radical–radical reaction kinetics: The O(3<i>P</i> <i>J</i>)+BrO reaction

Abstract

A novel dual laser flash photolysis-long path absorption-resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reaction O(3PJ)+BrO→k1Br(2PJ)+O2 as a function of temperature (231–328 K) and pressure (25–150 Torr) in N2 buffer gas. The experimental approach preserves the principal advantages of the flash photolysis method, i.e., complete absence of surface reactions and a wide range of accessible pressures, but also employs techniques which are characteristic of the discharge flow method, namely chemical titration as a means for deducing the absolute concentration of a radical reactant and use of multiple detection axes. We find that k1 is independent of pressure, and that the temperature dependence of k1 is adequately described by the Arrhenius expression k1(T)=1.91×10−11 exp(230/T) cm3 molecule−1 s−1; the absolute accuracy of measured values for k1 is estimated to vary from ±20% at T∼230 K to ±30% at T∼330 K. Our results demonstrate that the O(3PJ)+BrO rate coefficient is significantly faster than previously ‘‘guesstimated,’’ and suggest that the catalytic cycle with the O(3PJ)+BrO reaction as its rate-limiting step is the dominant stratospheric BrOx odd-oxygen destruction cycle at altitudes above 24 km.