A Direct Study of the Reactions of CH2 (X̃ 3B1)‐Radicals with Selected Hydrocarbons in the Temperature Range 296 K ≤ T ≤ 705 K

The kinetics of the reactions of CH2 (X 3B1)-radicals with five selected organic compounds has been studied in an isothermal discharge flow system in the temperature range 296 K ≤ T ≤ 705 K. Ground state CH2-radicals have been generated via the reaction O + CH2CO and monitored with a far infrared laser magnetic resonance spectrometer. The experimental results are described by the following Arrhenius expressions: Two basic reaction mechanisms, either direct H-atom abstraction by 3CH2 or thermal excitation of 3CH2 to the low lying a 1A1 state followed by consecutive reactions of 1CH2, are of importance. For acetaldehyde, isobutane, and propane direct H-atom abstraction by 3CH2 predominates. After separation of the small contribution attributed to the singlet reaction the following rate constants for the reactions of CH2 (X3B1) with acetaldehyde, isobutane, and propane are obtained: Presuming the reactions of 1CH2 with hydrocarbons are fast the thermal excitation mechanism dominates the reaction system in the cases of methane and ethane. The activation energy of EA (CH4) = 40 ± 8 kJ/mol measured for methane is concluded to he determined by the singlet-triplet energy splitting in CH2.

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