Radiolyse des n-alcanes en phase liquide
Contributions of radical and non-radical processes have been determined in the formation of radiolysis products of n-heptane, n-octane, n-nonane and n-decane in a large range of temperature. Calculations are based on the combination and the dismutation of radicals, both reactions having nearly the same importance. Hydrogen abstraction reactions become important above –25C°. Intermediate molecular weight products and dimers are formed by statistical combination of the various radicals resulting from C–C and C–H scission. At low temperature, low molecular weight products are formed by both radical and non-radical processes, the second one being more important (3/4 for alcanes and 2/3 for olefins). The yield of radicals increases with the chain length of the irradiated n-alkane and amounts to 4.5 for n-heptane and 6.8 for n-decane at –25°. This increase is due only to radicals from C–H scission, while the yield of radicals from C–C scission remains constant. Scission of CH2–CH2 bonds is favored for bonds inside the molecule, but this affect diminishes with chain length and CH2–CH2 rupture is equally probable at all positions for n-alcanes heavier than decane. Methyl C–H scission is 2.7 times less probable than methylene C–H scission. The radiolysis of mixtures of protonated and deuterated n-alcanes is shown to be able to give information concerning basic processes in radiation chemistry.