Multistructural variational transition state theory: Kinetics of the hydrogen abstraction from carbon-2 of 2-methyl-1-propanol by hydroperoxyl radical including all structures and torsional anharmonicity

We calculated the forward and reverse rate constants of the hydrogen abstraction reaction from carbon-2 of 2-methyl-1-propanol by hydroperoxyl radical over the temperature range 250-2400 K by using multistructural canonical variational transition state theory (MS-CVT) including both multiple-structure and torsional potential anharmonicity effects by the multistructural torsional anharmonicity (MS-T) method. In these calculations, multidimensional tunneling (MT) probabilities used to compute the tunneling transmission coefficients were evaluated by the small-curvature tunneling (SCT) approximation. Comparison with the rate constants obtained by the single-structural harmonic oscillator (SS-HO) approximation shows that multistructural anharmonicity increases the forward rate constants for all temperatures, but the reverse rate constants are reduced for temperatures lower than 430 K and increased for higher temperatures. The neglect of multistructural torsional anharmonicity would lead to errors of factors of 1.5, 8.8, and 13 at 300, 1000, and 2400 K, respectively, for the forward reaction, and would lead to errors of factors of 0.76, 3.0, and 6.0, respectively, at these temperatures for the reverse reaction.