Free radicals by mass spectrometry. IV. The rate of combination of methyl radicals

The rate of combination of methyl radicals produced by the thermal decomposition of mercury dimethyl has been studied with a free radical mass spectrometer over a large range of temperature (161\ub0 to 814\ub0C) and at one temperature (735\ub0C) over a range of total pressure from 4.8 mm to 18.5 mm. The combination was found to be complex, consisting of a second-order homogeneous reaction and a first-order, presumably heterogeneous reaction. Only the second-order reaction was studied in any detail. The rate constant or collision efficiency of this reaction was found to increase with decreasing temperature but showed no dependence on the carrier gas pressure. A negative temperature coefficient was found for the combination which, if expressed as an activation energy, was -2.2\ub10.5 kcal. It seems, however, more reasonable to regard this effect as a change in the effective collision diameter of the methyl radicals with temperature, the change being due to the van der Waals energy of attraction between the radicals.Peer reviewed: YesNRC publication: Ye

Free radicals by mass spectrometry. V. The ionization potentials of methyl, allyl, and benzyl radicals

The ionization potentials of methyl, allyl, and benzyl radicals have been measured directly by electron impact. The values found were methyl 9.95\ub10.03 ev, allyl 8,16\ub10.03 ev, and benzyl 7.73\ub10.08 ev. The radicals were produced by thermal decomposition of suitable compounds in a mass spectrometer designed for the study of free radicals. Reactions of the radicals after formation led to the expected dimers, but the disproportionation reactions were found to be negligibly slow.Peer reviewed: YesNRC publication: Ye

Free radicals by mass spectrometry. Part II. - The thermal decomposition of ethylene oxide, propyline oxide, dimethyl ether, and dioxane

The thermal decompositions of ethylene oxide, propylene oxide, dimethyl ether and dioxane in a stream of helium have been studied by means of a mass spectrometer designed to permit the measurement of free radical concentrations. With ethylene oxide it was found that each molecule decomposing gave rise to about 0.6 methyl radicals, and in propylene oxide the corresponding number had a lower limit of 0.36. Methyl radicals were also abundant in the decomposition of dimethyl ether. In the decomposition of dioxane only a small number of methyl radicals were found, and they probably come from a secondary reaction. No other radicals were detected, although formaldehyde was found to be a comparatively long-lived intermediate in the decomposition of dimethyl ether. The effect of the addition of nitric oxide on the decomposition of ethylene oxide was examined. Average values for the collision efficiency of the nitric oxide+methyl radical reaction at 950\ub0, and the methyl radical recombination reaction from 925\ub0 to 975\ub0 were found to be 2 7 10-4 and 2.5 7 10-2 respectively.Peer reviewed: YesNRC publication: Ye

The rate of combination of methyl radicals

Peer reviewed: YesNRC publication: Ye

General discussion

The Gerhard Herzberg fonds is held at the NRC Archives. Contact [email protected] for information about access.Le fonds Gerhard Herzberg est conserv\ue9 aux Archives du CNRC. Contactez [email protected] pour des informations sur l'acc\ue8s.Peer reviewed: YesNRC publication: Ye