Flash photolysis study of the CH sub 3 O sub 2 + CH sub 3 O sub 2 reaction: Rate constants and branching ratios from 248 to 573 K

Journal Article · Thu Jan 25 04:00:00 EST 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100365a035· OSTI ID:6614323

Lightfoot, P D; Lesclaux, R; Veyret, B ^[1]

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1. Universite de Bordeaux I., Talence (France)

The reactions 2CH{sub 3}O{sub 2} {yields} 2CH{sub 3}O + O{sub 2} (1a), 2CH{sub 3}O{sub 2} {yields} CH{sub 3}OH + HCHO + O{sub 2} (1b), and 2CH{sub 3}O{sub 2} {yields} CH{sub 3}OOCH{sub 3} + O{sub 2} (1c) have been studied at temperatures between 248 and 573 K. At temperatures above 373 K, the decay traces were distorted away from pure second order at short wavelengths (around 210 nm), owing to the presence of the hydroperoxy radicals formed via the nonterminating pathway (1a) and the subsequent rapid step CH{sub 3}O + O{sub 2} {yields} HCHO + HO{sub 2} (2). This distortion enabled the nonterminating/terminating branching ratio, {beta}, to be determined. Combining the present results with previously published work on the branching ratios gave ln {beta} = 3.80 {minus} 1,470/T. Thus, although reaction 1 acts as a termination reaction under atmospheric conditions, it largely serves to convert CH{sub 3}O{sub 2} into HO{sub 2} under combustion conditions. The temperature dependence of {beta} enabled the real rate constant for the reaction, k{sub 1}, to be obtained over the entire experimental temperature range, giving k{sub 1} = 1.3 {times} 10{sup {minus}13} exp(365/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, with {sigma}{sup 2}{sub A}/cm{sup 6} molecule{sup {minus}2} s{sup {minus}2} = 2.00 {times} 10{sup {minus}28}, {sigma}{sup 2}{sub E/R}/K{sup 2} = 1,712, and {sigma}{sup 2}{sub AE/R}/cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} = {minus} 5.61 {times} 10{sup {minus}13}. Absolute uncertainties, including contributions from both the experimental measurements and the dependence of k{sub 1} on various analysis parameters, are estimated to be 22%, independent of temperature. No dependence of either the branching ratio or k{sub 1} on the total pressure was found. The mechanism of the title reaction is discussed and the present results are compared with existing studies of alkylperoxy self-reactions.

• OSTI ID: 6614323
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:2; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400800 -- Combustion
Pyrolysis
& High-Temperature Chemistry
54 ENVIRONMENTAL SCIENCES
540120* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
ATMOSPHERIC CHEMISTRY
CHEMICAL REACTIONS
CHEMISTRY
COMBUSTION PRODUCTS
DATA
DATA ANALYSIS
DECOMPOSITION
EXPERIMENTAL DATA
HIGH TEMPERATURE
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
MEDIUM TEMPERATURE
NUMERICAL DATA
OZONE
PEROXY RADICALS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADICALS