Radiolysis of methane

Schuchmann H-P, von Sonntag C (1981) Photolysis at 185 nm of dimethyl ether in aqueous solution Involvement of the hydroxymethyl radical. J Photochem 16 289-295 Schuchmann H-P, von Sonntag C (1984) Methylperoxyl radicals a study ofthey-radiolysis of methane in oxygenated aqueous solutions. Z Naturforsch 39b 217—221 Schuchmann MN, von Sonntag C (1977) Radiation chemistry of carbohydrates. Part 14. Hydroxyl radical-induced oxidation of D-glucose in oxygenated aqueous solution. J Chem Soc Perkin Trans 2 1958-1963... 

The radiolysis of methane has been the subject of many investigations... 

The radiolysis of methane in the solid phase has been examined in several studies. ESR studies by Smaller and Matheson and by Wall eta/. have shown that methyl radicals and hydrogen atoms are formed in nearly equal quantities and that Gchj = 0.9. A product analysis in a study by Ausloos et shows that hydrogen and ethane are almost the only products of solid methane radiolysis at 20 or 77 °K. It seems that ethane is formed by both methylene insertion and by methyl radical combination, while hydrogen is formed by direct elimination and by bimolecular processes. A small quantity of ethylene formed at 20 °K is absent at 77 °K this has been attributed to the reaction of hydrogen atoms with ethylene at 77 °K (but not at 20 °K) to give ethyl radicals and finally higher products which are observed in increased yield at 77 °K. 

The rare-gas sensitized radiolysis of methane has been studied by Meisels et Ausloos et a/. - and by Aquilanti . In the presence of excess rare... 

The Radiolysis of Methane in a Wide-Range Radiolysis Source... 

We designed a novel three-compartment source (wide-range radiolysis source) for our research mass spectrometer, which was first used to study the radiolysis of methane. The present technique, employing flow, low pressure, localized ionization, and electric fields appears to be a straightforward approach to the problem, and we hoped that this technique would resolve some of the above discrepancies. Our objectives were to (a) determine the percent abundance of the various reactive primary species—ionic and neutral (b) ascertain the percent abundance of stable products under conditions that would minimize subsequent reactions of reactive stable products (c) calculate G values for these products (d) measure the relative contribution of ion-molecule reactions to the formation of stable products (e) obtain the threshold energies and yield curves for such products to assign their precursors and (f) postulate, from the above information and pressure studies, a mechanism for the production of the radiolytic products from methane. 

The results of these studies are given in Table I. The percent of all primary products is about equal for positive ions and neutral species (45% and 55%, respectively). Thus, it appears that any mechanism for producing stable products from the radiolysis of methane must include positive ions and neutral species. 

Figure 6. Abundance of the CHS and CtHs radicals produced by the radiolysis of methane with 100 e.v. electrons as a function of methane pressure...

Although this study of the radiolysis of methane was exploratory, it illustrated the usefulness of the wide-range radiolysis source, and our results contribute to the understanding of the radiolytic process which has been so controversial. Further development of the apparatus and techniques are contemplated, and the methane system will be studied further and in more detail. 

Most aspects of the radiolysis results are consistent with the interpretation that F-cyclobutane protects methane while methane simultaneously protects F-cyclobutane, particularly as regards free radical fragmentation. Molecular fragmentation to give C2F4 clearly persists in the mixtures, along with some processes of low yield giving C3 products. These protection effects can probably be explained in terms of ionic rather than free radical processes. As noted above, the radiolysis of methane is usually... 

Fig. 15. Radiolysis of methane adsorbed on 7-alumina expressed in terms of total product carbon (TPC, = chemisorbed CH4 + 2 (C2H4 + C2H6) + 3(C3H6 + C3H8)]. (a) Variation in TPC yield with radiation dose delivered to the CH3/AI2O3 system for samples previously outgassed at V, 623 K o, 673 K A, 723 K or 0, 923 K. (b) Variation in TPC yield with coverage by physisorbed methane on similarly pretreated A1203 samples dosed with methane and then 7-irradiated at two different dose rates of o, 1.1 and a, 0.29 M h 1. (c) Comparison of TPC desorption curves for 3 equivalently pretreated A12C>3 samples to which methane was added , before 7-irradiation at 77 K o, after 7-irradiation at 77 K but before warm-up A, after 7-irradiation at 77 K and warm-up to 300 K for 1 h.

The interaction of high-energy irradiation with alkanes leads, at the first stage of the process, to the excitation of the hydrocarbon molecule [3a]. Furthermore, the excited molecule decomposes to generate free radicals and carbenes. Radiolysis of methane produces ethane, ethylene, and higher... 

Primary CH3" and CH4 ions produced in the pulse radiolysis of methane react at every collision to form C2H5 and CH5 ions (equations 177), which do not react with methane but are intercepted by the reactive i-C D Q via the deuteride transfer reactions 178 to yield stable deuteriated hydrocarbons C2H5D, CD3H and C3D8. 

Yields of final products in the radiolysis of methane at a pressure of 1 bar... 

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