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Influence of Torsional Anharmonicity on the Reactions of Methyl Butanoate with Hydroperoxyl Radical
journal contribution
posted on 2020-10-08, 07:13 authored by Qinghui Meng, Lidong Zhang, Qinxue Chen, Yicheng Chi, Peng ZhangAn ab initio chemical kinetics study
of the reactions of methyl
butanoate (MB) with hydroperoxyl radical (HO2) is presented
in this paper. Particular interest is placed on determining the influences
of torsional anharmonicity and addition reaction on the rate constants
of hydrogen abstraction reactions. Stationary points on the potential
energy surface of MB + HO2 are calculated at the level
of QCISD(T)/CBS//B3LYP/6-311++G(d,p). The transition state theory
(TST) is used to calculate the high-pressure limit rate constants
of the hydrogen abstraction reactions over a board range of temperature
(500–2000 K). Anharmonicity of low-frequency torsional modes
is considered in the rate calculations by using the one-dimensional
hindered rotor approximation and the internal-coordinate multistructural
approximation; the latter is used as a higher-level theoretical method
to examine the applicability of the former in dealing with strongly
coupled torsional modes. The calculated rate constants are compared
with the available data from the literature and observed discrepancies
are analyzed in detail. An energetically lowest-lying addition reaction
with subsequent isomerization and decomposition reactions are identified
on the potential energy surface. The multiple-well Master equation
analysis shows that these reactions have a secondary influence on
the rate constants in the temperature range of interest.