A theoretical investigation of the gas-phase oxidation reaction of the saturated tert-butyl radical

The radical-radical reaction mechanisms and dynamics of ground-state atomic oxygen [O(³P)] with the saturated tert-butyl radical (t-C ₄H₉) are investigated using the density functional method and the complete basis set model. Two distinctive reaction pathways are predicted to be in competition: addition and abstraction. The barrierless addition of O(³P) to t-C₄H₉ leads to the formation of an energy-rich intermediate (OC₄H₉) on the lowest doublet potential energy surface, which undergoes subsequent direct elimination or isomerization-elimination leading to various products: C ₃H₆O + CH₃, iso-C₄H₈O + H, C₃H₇O + CH₂, and iso-C₄H ₈ + OH. The respective microscopic reaction processes examined with the aid of statistical calculations, predict that the major addition pathway is the formation of acetone (C₃H₆O) + CH₃ through a low-barrier, single-step cleavage. For the direct, barrierless H-atom abstraction mechanism producing iso-C₄H₈ (isobutene) + OH, which was recently reported in gas-phase crossed-beam investigations, the reaction is described in terms of both an abstraction process (major) and a short-lived addition dynamic complex (minor).