Pressure and temperature dependence of the gas-phase recombination of hydroxyl radicals
Rate constants for the reaction OH + OH + M ..-->.. H/sub 2/O/sub 2/ + M (M = N/sub 2/, H/sub 2/O) have been determined by using flash photolysis of H/sub 2/O vapor in combination with quantitative OH resonance spectrometry. For M = N/sub 2/ experiments were performed at 253, 298, and 353 K and at pressures between 26 and 1100 mbar. Under these conditions the reaction is found to be primarily in the low-pressure limit with k/sub 1,N/sub 2///sup 0/ (T = 298 K) = (6.9/sub -2.5//sup +1.4/) x 10/sup -31/ cm/sup 6//s and a temperature dependence of T/sup -0.8/. Both the absolute value of k/sub 1,N/sub 2// and its temperature variation are in very satisfactory agreement with theoretical predictions and extrapolations from high-temperature dissociation data. A pressure falloff of k/sub 1,N/sub 2// is also observed. On the basis of a theoretical analysis of the falloff behavior, a high-pressure limiting rate coefficient of k/sub 1/infinity = 1.5 x 10/sup -11/ cm/sup 3//s, independent of temperature, is predicted. From experiments in N/sub 2//H/sub 2/O mixtures with /kappa cur//sub H/sub 2/O/ = 0.11 at pressures up to 140 mbar a low-pressure limiting rate coefficient for H/sub 2/O as a third body of k/sub 1,H/sub 2/O//sup 0/ (T = 298 K) = (4.0 /sub -2.0//sup +1.3/) x 10/sup -30/ cm/sup 6//s is obtained.
- Research Organization:
- Universitaet Goettingen (West Germany)
- OSTI ID:
- 6289412
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:14; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
400800 -- Combustion
Pyrolysis
& High-Temperature Chemistry
500200 -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
EXPERIMENTAL DATA
HYDROGEN COMPOUNDS
HYDROXYL RADICALS
INFORMATION
KINETICS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PRESSURE DEPENDENCE
RADICALS
REACTION KINETICS
RECOMBINATION
TEMPERATURE DEPENDENCE
WATER