Theoretical kinetics for the decomposition of iso -butanol and related (CH3)2ĊH+ĊH2OH reactions

The potential energy surface for the thermal decomposition of iso  -butanol has been investigated using high level ab initio electronic structure methods. Temperature and pressure dependent rate coefficients for the three channels with the lower energy barriers, forming (CH3)2ĊH+ĊH2OH (k1), CH3ĊHCH2OH+ĊH3 (k2) and (CH3)2C=CH2 + H2O (k3) were computed with the master equation method employing ab initio transition state theory estimates for the microcanonical rate coefficients. The two radical forming channels were treated with variable-reaction-coordinate transition state theory employing directly sampled CASPT2(2e,2o)/cc-pVDZ orientation dependent interaction energies coupled with one-dimensional basis set and relaxation corrections. The other channel was treated with conventional TST including Eckart tunneling and one-dimensional hindered rotor corrections. For temperatures higher than 1000 K and pressures of 1 Torr or greater, the direct C–C bond fission forming (CH3)2ĊH+ĊH2OH is dominant, while the formations of CH3ĊHCH2OH+ĊH3 and (CH3)2C=CH2 + H2O together contribute less than 20%. The bi-molecular recombination of (CH3)2ĊH+ĊH2OH has also been investigated, with the formation of iso  -butanol found to be dominant at high pressure and the production of CH3ĊHCH2OH+ĊH3 favored at low pressure.