Formation of methoxy and hydroxymethyl free radicals in selected elementary reactions
- Hungarian Academy of Sciences, Budapest (Hungary). Central Research Inst. for Chemistry
- Max-Planck-Institut fuer Stroemungsforschung, Goettingen (Germany)
The fast flow technique combined with laser-induced fluorescence (LIF) and laser magnetic resonance (LMR) detections have been used to obtain branching ratios for CH{sub 3}O and CH{sub 2}OH formation, respectively, in various reactions. A detailed study of the product yields showed that reaction F + CH{sub 3}ONO = FNO + CH{sub 3}O is a clean methoxy radical source at low temperature that gives CH{sub 3}O with practically 100 % efficiency. The branching ratios for CH{sub 3}O and CH{sub 2}OH formation in the reaction of F with CH{sub 3}OH are k{sub 1a}/(k{sub 1a} + k{sub 1b}) = 0.57 {+-} 0.05 and k{sub 1b}/(k{sub 1a} + k{sub 1b}) = 0.41 {+-} 0.05, respectively, between 300 and 600 K independent of temperature; F + CH{sub 3}OH = HF + CH{sub 3}O (1a), F + CH{sub 3}OH = HF + CH{sub 2}OH (1b). The branching ratios for product radical formation in reactions X + CH{sub 3}OH = HX + CH{sub 3}O and X + CH{sub 3}OH = HX + CH{sub 2}OH (where X = F, OH, and Cl) were studied between 298 and 612 K. The considerable decrease of exothermicity in the order of F, OH, and Cl reactions is expected to go with a decrease in reactivity and a simultaneous increase in selectivity, which is indeed experienced for reactions F + CH{sub 3}OH and OH + CH{sub 3}OH. However, the reaction Cl + CH{sub 3}OH was found to be a ``high reactivity high selectivity`` process yielding CH{sub 2}OH radicals with practically 100% yield up to about 500 K. The fast reaction and the relatively small temperature dependences of the branching ratios indicate that some specific effects govern the kinetics of this reaction. Combustion implications and utilization of the results in kinetic experiments are discussed.
- OSTI ID:
- 93226
- Report Number(s):
- CONF-940711--
- Country of Publication:
- United States
- Language:
- English
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