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), Vol. 91:5
- Country of Publication:
- United States
- Language:
- English
Similar Records
Slow chain reactions of Br/sub 2/ and Cl/sub 2/ with HI: Multiple state analysis and vibrational relaxation of HBr(v = 2) and HCl(v = 1--4)
Laser magnetic resonance, resonance fluorescence, and resonance absorption studies of the reaction kinetics of O + OH. -->. H + O/sub 2/, O + HO/sub 2/. -->. OH + O/sub 2/, N + OH. -->. H + NO, and N + HO/sub 2/. -->. products at 300 K between 1 and 5 torr
Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
BROMIDES
CHEMICAL REACTIONS
HYDROGEN COMPOUNDS
HYDROGEN PEROXIDE
HYDROPEROXY RADICALS
OXYGEN
ATMOSPHERIC CHEMISTRY
BROMINE
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
FLUORESCENCE
LASERS
LOW TEMPERATURE
MAGNETIC RESONANCE
MEDIUM TEMPERATURE
REACTION INTERMEDIATES
RESONANCE ABSORPTION
ABSORPTION
BROMINE COMPOUNDS
CHEMISTRY
DATA
ELEMENTS
HALIDES
HALOGEN COMPOUNDS
HALOGENS
INFORMATION
KINETICS
LUMINESCENCE
NONMETALS
NUMERICAL DATA
OXYGEN COMPOUNDS
PEROXIDES
RADICALS
REACTION KINETICS
RESONANCE
400201* - Chemical & Physicochemical Properties
500100 - Environment
Atmospheric- Basic Studies- (-1989)