Kinetics of the HO2+BrO reaction over the temperature range 233–348 K

Abstract

The reaction is the rate-limiting step in a key catalytic ozone destruction cycle in the lower stratosphere. BrO ] HO 2 ] products In this study a discharge-Ñow reactor coupled with molecular beam mass spectrometry has been used to study the BrO ] HO 2 reaction over the temperature range 233È348 K. Rate constants were measured under pseudo-Ðrst-order conditions in separate experiments with Ðrst and then BrO in excess in an e †ort to identify possible complications in the reaction conditions. At HO 2 298 K, the rate constant was determined to be (1.73^0.61) ] 10~11 cm3 molecule~1 s~1 with in excess and HO 2 (2.05^0.64) ] 10~11 cm3 molecule~1 s~1 with BrO in excess. The combined results of the temperature-dependent experiments gave the following Ðt to the Arrhenius expression : k \ (3.13^0.33) ] 10~12 exp(536^206/T ) where the quoted uncertainties represent two standard deviations. The reaction mechanism is discussed in light of recent ab initio results on the thermochemistry of isomers of possible reaction intermediates.

Rate coefficient for the BrO + HO2 reaction at 298 K

“…It was not possible to obtain HO 2 concentrations reliably by the same method, due to the contaminating absorption arising from the significant concentrations of O 3 required to stoichiometrically convert Br atoms to BrO radicals. The initial concentration of HO 2 radicals generated via reactions (6), (7) and (8) was however constrained: An actinometric calibration of Cl 2 photolysis (and hence Cl atom generation and subsequent HO 2 production) was performed by monitoring the production of methylperoxy radicals in separate back-to-back experiments employing the photolysis of (known) concentrations of Cl 2 in the presence of O 2 and CH 4 .…”

State-resolved two-photon laser induced fluorescence detection of BrO

“…1 This importance of halogen monoxide free radicals for the atmosphere has motivated numerous studies addressing ClO, BrO, and IO. [2][3][4][5][6] In most investigations ClO and BrO radicals are observed by absorption using their well-known A 2 ⌸ -X 2 ⌸ bands. In evaluating the gas-phase dynamics and mechanistics, however, detection methods which are more sensitive and state resolved in nature are required.…”

Global warming potential assessment for CF3OCF = CF2

“…Note that the drawing only illustrates the relative position of the instrument, not the actual size or distance of the instrumental elements. The DF/MS system in present study has been described previously [Li et al, 1997;Li, 1999], and is only briefly discussed here. The reactor consisted of an 80-cmlong, 5.08-cm-ID Pyrex tube coated with halocarbon wax to reduce OH wall losses.…”