LASER FLASH-PHOTOLYSIS STUDIES OF RADICAL-RADICAL REACTION-KINETICS -THE HO2+BRO REACTION

Laser flash photolysis of Cl-2/CH3OH/O-2/Br-2/O-3/N-2 mixtures at 308 nm has been coupled with simultaneous time-resolved detection of HO2 ( by infrared tunable diode laser absorption spectroscopy) and BrO (by u ltraviolet absorption spectroscopy) to investigate the kinetics of the important stratospheric reaction HO2 + BrO -->products at 296 +/- 3 K in N-2 buffer gas at pressures of 12 and 25 Torr. All experiments wer e performed under near pseudo-first-order conditions with HO2 in exces s over BrO. The HOr + BrO rate coefficient is found to be k(1) = (2.0 +/- 0.6) x 10(-11) cm(3) molecule(-1) s(-1), with the primary source o f uncertainty being knowledge of the infrared line strength(s) require d to convert measured HO2 absorbances to absolute concentrations. The rate coefficient for the reaction HO2 +/- HO2 --> H2O2 + O-2 derived b ased on infrared absorption measurements of the HO2 concentration is c onsistent with the currently accepted value. The results reported in t his study are compared with other recent studies of HO2 + BrO kinetics , and their implications for our understanding of stratospheric chemis try are discussed.