Formation of methoxy and hydroxymethyl free radicals in selected elementary reactions

S. Dóbé, T. Bérces, F. Temps, H. Gg Wagner, H. Ziemer

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The fast flow technique combined with laser-induced fluorescence (LIF) and laser magnetic resonance(LMR) detections have been used to obtain branching ratios for CH3O and CH2OH formation respectively, in various reactions. A detailed study of the product yields showed that reaction F+CH3ONO→ FNO+CH3O is a clean methoxy radical source at low temperature that gives CH3O with practically 100% efficiency. The branching ratios for CH3O and CH2OH formation in the reaction of F with CH3OH are k1a/(k1a+k1b)=0.57±0.05 and k1b/(k1a+k1b)=0.41±0.05, respectively, between 300 and 600 K independent of temperature; F+CH3OH→HF+CH3O (1a), F+CH3OH→HX+CH2OH (1b). The branching ratios for product radical formation in reactions X+CH3OH→HX+CH3O and X+ CH3OH→HX+CH2OH (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+CH3OH and OH+CH3OH. However, the reaction Cl+CH3OH was found to be a "high reactivity high selectivity" process yielding CH2OH 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.

Original languageEnglish
Pages (from-to)775-781
Number of pages7
JournalSymposium (International) on Combustion
Volume25
Issue number1
DOIs
Publication statusPublished - 1994

Fingerprint

Free radicals
free radicals
Free Radicals
Kinetics
Lasers
Magnetic resonance
Temperature
Fluorescence
reactivity
selectivity
Experiments
kinetics
products
laser induced fluorescence
magnetic resonance
temperature dependence

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Fluid Flow and Transfer Processes
  • Physical and Theoretical Chemistry
  • Energy Engineering and Power Technology
  • Fuel Technology
  • Mechanical Engineering

Cite this

Formation of methoxy and hydroxymethyl free radicals in selected elementary reactions. / Dóbé, S.; Bérces, T.; Temps, F.; Wagner, H. Gg; Ziemer, H.

In: Symposium (International) on Combustion, Vol. 25, No. 1, 1994, p. 775-781.

Research output: Contribution to journalArticle

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abstract = "The fast flow technique combined with laser-induced fluorescence (LIF) and laser magnetic resonance(LMR) detections have been used to obtain branching ratios for CH3O and CH2OH formation respectively, in various reactions. A detailed study of the product yields showed that reaction F+CH3ONO→ FNO+CH3O is a clean methoxy radical source at low temperature that gives CH3O with practically 100{\%} efficiency. The branching ratios for CH3O and CH2OH formation in the reaction of F with CH3OH are k1a/(k1a+k1b)=0.57±0.05 and k1b/(k1a+k1b)=0.41±0.05, respectively, between 300 and 600 K independent of temperature; F+CH3OH→HF+CH3O (1a), F+CH3OH→HX+CH2OH (1b). The branching ratios for product radical formation in reactions X+CH3OH→HX+CH3O and X+ CH3OH→HX+CH2OH (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+CH3OH and OH+CH3OH. However, the reaction Cl+CH3OH was found to be a {"}high reactivity high selectivity{"} process yielding CH2OH 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.",
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AB - The fast flow technique combined with laser-induced fluorescence (LIF) and laser magnetic resonance(LMR) detections have been used to obtain branching ratios for CH3O and CH2OH formation respectively, in various reactions. A detailed study of the product yields showed that reaction F+CH3ONO→ FNO+CH3O is a clean methoxy radical source at low temperature that gives CH3O with practically 100% efficiency. The branching ratios for CH3O and CH2OH formation in the reaction of F with CH3OH are k1a/(k1a+k1b)=0.57±0.05 and k1b/(k1a+k1b)=0.41±0.05, respectively, between 300 and 600 K independent of temperature; F+CH3OH→HF+CH3O (1a), F+CH3OH→HX+CH2OH (1b). The branching ratios for product radical formation in reactions X+CH3OH→HX+CH3O and X+ CH3OH→HX+CH2OH (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+CH3OH and OH+CH3OH. However, the reaction Cl+CH3OH was found to be a "high reactivity high selectivity" process yielding CH2OH 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.

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