The 2288 Å Photolysis of Hydrogen Iodide in the Presence of Ethylene and Propylene

Abstract

Abstract The photolysis of hydrogen iodide at 2288 Å has been investigated in the presence of ethylene or propylene. The combinations studied were DI-C2H4, HI-C2D4, and DI-C3H6. In all combinations, the formation of a large amount of HD was observed; this may be attributed to the reaction of hot hydrogen atoms. The pressure dependence of the relative yields of HD and total hydrogen suggested that, of the two possible hot hydrogen atom reactions with ethylene, the abstraction reaction, D*+C2H4→C2H3+HD (2) does not occur, while the substitution reaction, D*+C2H4→C2H3D+H (3) is the important process. In the case of propylene, however, the abstraction of H by D* is important for the formation of HD. The measured ratios of C2H3D/HD in the DI–C2H4 system and of C2D3H/HD in the HI–C2D4 system were consistent with the above conclusion. Reaction (3) is probably not a real substitution reaction, but a combination of the addition reaction of a hydrogen atom to ethylene and the rapid decomposition of the excited ethyl radical produced.