Mercury-photosensitized decomposition of dimethyl ether. Part III. The combination of radicals

Abstract

As part of the study of the mercury-photosensitized decomposition of dimethyl ether, the combination of methyl radicals has been investigated in the temperature range 200 to 300 °C and at pressures between 3 and 300 mm Hg. For pressures of less than 100 mm the second-order rate coefficient for the combination of methyl radicals shows a pressure dependence. The pressure dependence agrees qualitatively with that observed by others, but occurs at somewhat higher pressures. Calculations for the Kassel equation using the Arrhenius parameters for ethane decomposition and fitted to the pressure dependence of the methyl radical combination show that the number of effective modes for ethane decomposition is 8 or 9. Carbon dioxide was found to be a quite ineffective third body for energy transfer. The results for the mercury-photosensitized decomposition of dimethyl ether have also been analyzed to obtain information about the combination of methyl radicals with methoxymethyl radicals. The combination of these radicals becomes pressure dependent at pressures less than about 15 mm. Kassel integrations based on the rate constant [Formula: see text]for the unimolecular decomposition of methyl ethyl ether at the C—C bond, and fitted to the observed pressure dependence of the combination reaction, lead to s = 10 for these reactions.The rate constant for the abstraction of a hydrogen atom by a methyl radical from dimethyl ether was found to be [Formula: see text]