Vacuum Ultraviolet Photochemistry. VII. Photolysis of n-Butane

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Abstract
The photolysis of n‐butane has been carried out at room temperature at the Xe resonance lines. A few photolyses have been done at the Kr resonance lines. The isotopic analyses of products—hydrogen, methane, ethane, and ethylene—produced in the photolysis of mixtures of C4H10+C4D10 and of CH3CD2CD2CH3 were made, in the presence and the absence of 10% NO, to obtain information on the detailed modes of decomposition. From these results, it was concluded that, at the Xe lines: (1) Hydrogen is detached mainly by a molecular process C 4 H 10 → H 2 + C 4 H 8 and preferentially from the inside carbon atoms. (2) Methane, amounting to 5% of hydrogen, is produced both from the methyl radical and probably from three different molecular processes. (3) Ethylene is produced chiefly by the molecular process CH 3 CD 2 CD 2 CH 3 →2 CH 2 CD 2 +2 H . (4) Ethane is produced by molecular elimination as well as the combination of methyl radicals CH 3 CD 2 CD 2 CH 3 → CH 3 CD 3 + CH 3 CD , 2 CH 3 → C 2 H 6 . Other unsaturated hydrocarbons are produced largely by molecular processes, whereas saturated hydrocarbons are produced mainly from free‐radical processes. Relative probabilities of the primary processes are assessed.