NASA - National Aeronautics and Space Administration

A novel dual laser flash photolysis-long path absorption-resonance fluorescence technique has been

k1 employed to study the kinetics of the important stratospheric reaction O( 3 P J )ϩBrO→ Br( 2 P J ) ϩO2 as a function of temperature ͑231–328 K͒ and pressure ͑25–150 Torr͒ 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 k 1 is independent of pressure, and that the temperature dependence of k 1 is adequately described by the Arrhenius expression k 1 (T)ϭ1.91ϫ10Ϫ11 exp͑230/T͒ cm3 moleculeϪ1 sϪ1; the absolute accuracy of measured values for k 1 is estimated to vary from Ϯ20% at Tϳ230 K to Ϯ30% at Tϳ330 K. Our results demonstrate that the O͑3P J ͒ϩBrO rate coefficient is significantly faster than previously ‘‘guesstimated,’’ and suggest that the catalytic cycle with the O͑3P J ͒ϩBrO reaction as its rate-limiting step is the dominant stratospheric BrOx odd-oxygen destruction cycle at altitudes above 24 km.