Vacuum Ultraviolet Photochemistry. IV. Photolysis of Propane

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Abstract
The direct photolysis of propane has been carried out in the vacuum ultraviolet region, at room temperature. Isotopic analyses lead to the conclusion that hydrogen and methane are formed almost entirely by molecular detachment processes. Among the three observed modes of hydrogen detachment CH 3 CH 2 CH 3 → CH 3 CCH 3 + H 2 , CH 3 CH 2 CH 3 → CHCH 2 CH 3 + H 2 , CH 3 CH 2 CH 3 → CH 2 CHCH 3 + H 2 . Process (1), the detachment from the central carbon atom, is most important when the exciting wavelengths are the Xe resonance lines, whereas process (2) increases in importance with the Kr lines. Two modes of methane detachment were observed, CH 3 CH 2 CH 3 → CH 3 CH + CH 4 , CH 3 CH 2 CH 3 → CH 2 CH 2 + CH 4 , in which process (5) is more important at both wavelengths. It has been shown that ethylene is formed almost equally from the molecular detachment process and from the disproportionation of of ethyl radicals. Ethane is formed from the disproportionation of ethyl radicals as well as from the association of methyl radicals, the former being more important. The processes (1) to (6), along with two additional processes, CH 3 CH 2 CH 3 → H + C 3 H 7 , CH 3 CH 2 CH 3 → CH 3 + C 2 H 5 , followed by secondary reactions of radicals, can reasonably account for the formation of the photolytic products.

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