Laser Flash Photolysis Studies of Radical-Radical Reaction Kinetics: The HO_2 + BrO Reaction

摘要

Laser flash photolysis of Cl_2/CH_3OH/O_2/Br_2/O_3/N_2 mixtures at 308 nm has been coupled with simultaneous time-resolved detection of HO_2 (by infrared tunable diode laser absorption spectroscopy) and BrO (by ultraviolet absorption spectroscopy) to investigate the kinetics of the important stratospheric reaction HO_2 + BrO → products at 296 ± 3 K in N_2 buffer gas at pressures of 12 and 25 Torr. All experiments were performed under near pseudo-first-order conditions with HO_2 in excess over BrO. The HO_2 + BrO rate coefficient is found to be k_1 = (2.0 ± 0.6) * 10~(-11) cm~3 molecule~(1) s~(-1), with the primary source of uncertainty being knowledge of the infrared line strength(s) required to convert measured HO_2 absorbances to absolute concentrations. The rate coefficient for the reaction HO_2 + HO_2 → H_2O_2 + O_2 derived based on infrared absorption measurements of the HO_2 concentration is consistent with the currently accepted value. The results reported in this study are compared with other recent studies of HO_2 + BrO kinetics, and their implications for our understanding of stratospheric chemistry are discussed.