The reaction of oxygen atoms generated by mercury-sensitized decomposition of nitrous oxide with the fluoro-olefin yields almost wholly the addition products 2-(trifluoromethyl)-propylene oxide and 2-(trifluoromethyl)-propionaldehyde over the pressure range 10–500mm Hg. The rate constant for the reaction relative to that for butene–1 has been measured as 0.077.