Kinetics and Mechanism of the BrO + HO2 Reaction

Abstract

Using the discharge flow-mass spectrometric technique, the kinetics and mechanism of the BrO + HOa reaction have been investigated in the temperature range 233-344 K. With an excess of H02 over BrO, the rate constant was found to be kl = (4.77 f 0.32) x exp[(580 f 100) / r] cm3 molecule-' s-l. The reaction may proceed via two channels: BrO + H02 -HOBr + 0 2 (la) and BrO + HO2 -HBr + 0 3 (lb).Over the whole temperature range, HOBr was observed as the major product, whereas an upper limit was measured for channel l b from the absence of detection of 0 3 : kldkl .c 1.5%. The potential implications of these data are briefly discussed in relation to the stratospheric bromine/ozone interaction.

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

“…8,19 The detailed formation mechanisms are not known but wall reactions play a key role in the formation and interconversion of the bromine oxides, and the primary products may be both OBrO and The Br 2 O.20 surface reactions appear to require the presence of O(3P) and/or metastable oxygen 1&) from the microwave dis-O 2 (1*, charge. In order to characterize the products of the wall reactions occurring in the Ñow reactor, separate experiments were carried out using similar discharge-Ñow systems coupled to UVÈVIS and submillimeter absorption spectrometers.…”

Kinetics of the BrO + HO2 reaction over the temperature range T = 246–314 K

“…BrO was produced by the O( 3 P) + Aside from the overall kinetics of reaction (1), the potential branching between channels (1a) and (1b) has also been investigated previously. Neither Bedjanian et al 25 or Larichev et al 21 detected any evidence for ozone formation via channel (1b), therefore reporting branching ratios of < 0.015 and < 0.004 from this channel respectively, based upon detection limits. This is supported by theory, from, for example, Guha and Francisco 27 and Kaltsoyannis and Rowley 28 .…”

“…4 The rate constant we report is: Red squares are data inferred from spectroscopic fits. Poulet et al 19 Bridier et al 20 Larichev et al 21 Elrod et al 22 Li et al 23 Cronkhite et al 24 Bedjanian et al 25 Bloss et al …”

“…19 Bridier et al k1 via the discharge flow mass spectrometric method over the temperature range T = 233 -344 K with an excess of HO2 over BrO. 21 Elrod et al studied k1 in a turbulent discharge flow system at a total pressure of p = 130 mbar at T = 298 -210 K using detection, following titration of radicals, by chemical ionisation mass spectrometry. 22 As with previous discharge flow studies, k1 was determined by monitoring the BrO radical concentrations in an excess of HO2 radicals.…”

Stratospheric HBr concentration profile obtained from far‐infrared emission spectroscopy

“…In situ measurements of BrO have been reported from a polar balloon flight by Toohey has been proposed as a reaction pathway which could increase HBr and thus serve to reduce the bromine ODP. A recent laboratory measurement of this reaction set yielded an upper limit of 1.5% for reaction (2) compared to reaction (1) at stratospheric temperatures (Larichev et al, 1995), while an earlier indirect measurement using the reverse of reaction (2) resulted in a much smaller branching limit of < 0.01% (Mellouki et al , 1994). An early workshop on methyl bromide in 1992 identified significant differences between model estimates of stratospheric I-lBr and the limited experimental data then available (Park et al 1989;Traub et al, 1992).…”