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( 3 P)] with the saturated tert ‐butyl radical ( t ‐C 4 H 9 ) 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( 3 P) to t ‐C 4 H 9 leads to the formation of an energy‐rich intermediate (OC 4 H 9 ) on the lowest doublet potential energy surface, which undergoes subsequent direct elimination or isomerization–elimination leading to various products: C 3 H 6 O+CH 3 , iso ‐C 4 H 8 O+H, C 3 H 7 O+CH 2 , and iso ‐C 4 H 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 (C 3 H 6 O)+CH 3 through a low‐barrier, single‐step cleavage. For the direct, barrierless H‐atom abstraction mechanism producing iso ‐C 4 H 8 (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).