[en] The gas-phase reactions of ground state (triplet) oxygen atoms with 2-methylpropene-d₀, -1-d₁, and -1-1-d₂ have been studied. The oxygen atoms were generated by the mercury photosensitized decomposition of nitrous oxide. Vinylic deuterium substitution of the olefin increases the epoxide yield and decreases the yields of carbonyl products. The rate of O(³P) addition to the olefin shows a small inverse secondary isotope effect. A primary isotope effect upon the relative migratory aptitudes of hydrogen vs. deuterium rearrangement in the formation of 2-methylpropanal was observed