Mechanism and kinetics of Br + HO/sub 2/. -->. HBr + O/sub 2/ and Br + H/sub 2/O/sub 2/. -->. products over the temperature range 260-390 K
A discharge flow system employing simultaneous, direct detection of HO/sub 2/ and Br using laser magnetic resonance and resonance fluorescence, respectively, is used to study the kinetics of the title reactions. Over the temperature range 260 to 390 K, decays of HO/sub 2/ in excess Br yield the rate constant k/sub 1/ = (1.4 +/- 0.2) x 10/sup -11/ exp((-590 +/- 140)/T) cm/sup 3/ molecule/sup -1/ s/sup -1/ for Br + HO/sub 2/ ..-->.. HBr + O/sub 2/. Experiments were carried out at 0.8 to 2 Torr total pressure in helium and in argon with multiple Br sources. The cited uncertainties include an estimate of the systematic errors at the 95% confidence level. Additional studies place an upper limit of 5 x 10/sup -16/ cm/sup 3/ molecule/sup -1/ s/sup -1/ on the overall rate constant and product channels forming OH and HO/sub 2/ for the reaction Br + H/sub 2/O/sub 2/ ..-->.. products from 298 to 378 K. These results, in conjunction with data from other HO/sub 2/ reactions, suggest that X + HO/sub 2/ ..-->.. HX + O/sub 2/ reactions (where X = F, Cl, Br, and OH) proceed by direct attack on the H-O sigma bond, rather than by radical addition to form a (HOOX)* intermediate followed by rearrangement and elimination of HX and O/sub 2/ from a modified four-center transition state. The implications of these studies for stratospheric chemistry are discussed.
- Research Organization:
- Harvard Univ., Cambridge, MA
- OSTI ID:
- 6808741
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 91:5; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
500100 -- Environment
Atmospheric-- Basic Studies-- (-1989)
54 ENVIRONMENTAL SCIENCES
ABSORPTION
ATMOSPHERIC CHEMISTRY
BROMIDES
BROMINE
BROMINE COMPOUNDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
DATA
ELEMENTS
EXPERIMENTAL DATA
FLUORESCENCE
HALIDES
HALOGEN COMPOUNDS
HALOGENS
HYDROGEN COMPOUNDS
HYDROGEN PEROXIDE
HYDROPEROXY RADICALS
INFORMATION
KINETICS
LASERS
LOW TEMPERATURE
LUMINESCENCE
MAGNETIC RESONANCE
MEDIUM TEMPERATURE
NONMETALS
NUMERICAL DATA
OXYGEN
OXYGEN COMPOUNDS
PEROXIDES
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
RESONANCE
RESONANCE ABSORPTION