Ab initio studies of the isomerization and decomposition reactions of the 1-butoxy radical

The unimolecular reactions of the 1-butoxy radical, a prototype of atmosphe rically important alkoxy radicals, are studied. The structures of the isome rs of the C4H9O radical and the transition structures of the isomerization and main decomposition reactions of 1-butoxy are determined by ab initio qu antum chemical methods. The energy-dependent rate coefficients of the unimo lecular reactions involved were obtained in RRKM calculations. The threshol d energy for the fastest channel, the 1,5 intramolecular H-atom transfer is 8.12, 9.23, 9.16, and 9.51 kcal mol(-1) according to the MP-SAC2, BAC-MP4, DFT, and an additively corrected MP4 method, respectively. For the beta-C- C dissociation reaction we found a barrier of 16.03, 13.34, and 12.39 kcal mol(-1) at the BAC-MP4, DFT, and additively corrected MP4 level. The barrie r height for the 1,4 isomerization is close to that of the C-C bond rupture . The fastest reaction of the radical is isomerization involving a six-memb er transition structure, converting the alkoxy radical into an OH-substitut ed alkyl radical. The decomposition reaction can compete with the 1,5 isome rization step at high excitation or at combustion temperatures.