A Theoretical Kinetic Study of H Atom Abstraction Reactions from Four Branched Pentanol Isomers by ȮH Radicals: from Electronic Structure to Combustion Modeling Applications

A detailed high-level ab initio calculation on H atom abstraction (HAA) reactions from four branched pentanol isomers of 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, and 2,2-dimethyl-1-propanol by ȮH radicals has been performed in this work. Geometry optimization, frequency calculations, and zero-point energy (ZPE) corrections were carried out at the M06-2X/6-311++G(d,p) level of theory. The intrinsic reaction coordinate (IRC) calculation was performed at the same level of theory to confirm the transition state connection. Low-frequency torsional modes were treated as one-dimensional hindered rotors at the M06-2X/6-311++G(d,p) level of theory. Single point energy (SPE) calculations for species involved on the potential energy surfaces were obtained at the QCISD(T)/cc-pVDZ, QCISD(T)/cc-pVTZ, MP2/cc-pVDZ, MP2/cc-pVTZ, and MP2/cc-pVQZ levels of theory and then extrapolated to the complete basis set (CBS). The multireference complete-active-space second-order perturbation theory, CASPT2(5e,5o) method using cc-pVTZ and cc-pVQZ basis sets and extrapolating to the CASPT2(5e,5o)/CBS, was applied to calculate the single point energies for the reaction channels in which the T1 diagnostic value of transition state was larger than 0.035. Variational transition state theory (VTST) with the asymmetric Eckart tunnelling model was employed to calculate the rate constants for all of the 19 reaction channels in the temperature range of 500-2000 K. Branching ratios and rate rules were also investigated. The kinetic data calculated in this work can be used to develop combustion kinetic models for these pentanol isomers to predict their combustion properties.