Methylperoxyl Radicals: A Study of the γ-Radiolysis of Methane in Oxygenated Aqueous Solutions

A product study has been made of the γ-radiolysis of aqueous methane solutions that also contained nitrous oxide and oxygen. Formaldehyde (G = 2.8), hydrogen peroxide (G = 2.1), methanol (G = 1.5), methylhydroperoxide (G = 0.8), formic acid (G = 0.3), and dimethylperoxide (G = 0.1) were found. In alkaline solutions (pH 8, 10 -3 M phosphate buffer), the formaldehyde yield rises to G = 3.2, while the formic acid yield falls to almost zero (G = 0.05). The initial precursor of the carbon-containing products is the methylperoxyl radical. The methylperoxyl radicals decay through a short-lived tetroxide along various pathways. The most prominent one leads to formaldehyde, methanol and oxygen. Methoxyl radicals (and oxygen) are also formed and, after rearrangement into hydroxymethyl radicals and their conversion into hydroxymethylperoxyl radicals, eventually yield formic acid and probably further formaldehyde. A route to formaldehyd and hydrogen peroxide is also envisaged. Methylhydroperoxide is formed in the reaction of methylperoxyl radicals with HO 2 /O 2 ·̄ radicals (from radiolytic H atoms and the unimolecular decay of the hydroxymethylperoxyl radical)