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• Investigation of the Thermal Decomposition of Ketene and of the Reaction CH2+H2 ⇔ CH3+H

G. Friedrichs and H.Gg. Wagner
Z. Phys. Chem. 215, 1601-1623 (2001)

 

Using frequency modulation (FM) spectroscopy singlet methylene radicals have been detected for the first time behind shock waves. The thermal decomposition of ketene served as source for metylene radicals at temperatures from 1905 to 2780 K and pressures around 450 mbar and was described by a complex reaction mechanism. For the unimolecular decomposition reaction, (1) CH2CO+M→ CH2 + CO +M, the rate constants obtained are:

k1 = (9.5± 5.7)· 1015 · exp[-(244± 25) kJmol-1 / R T] cm3mol-1s-1

As a first study of a methylene reaction at high temperatures by diretly tracing methylene the reaction of methylene with hydrogen, (8+9) 1,3CH2+H2 ⇔ CH3+H was investigated at temperatures from 1930 to 2455 K at pressures around 500 mbar. For the total rate constant, singlet and triplet methylene reaction, a temperature independent rate constant was obtained:

log(k8+9 / (cm3mol-1s-1)) = 13.89±0.26

A comparison with low temperature literature data and the systematics of activation energies of triplet methylene reactions allowed for a consistent description of singlet and triplet contribution and of forward and reverse reaction.

 

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