A kinetics study on hydrogen abstraction reactions of cyclopentane by hydrogen, methyl, and ethyl radicals

Hydrogen abstraction reactions of (cyclo)alkanes by radicals play a fundamental role in both combustion and atmospheric chemistry. In this work, we select three common radicals in the pyrolysis of hydrocarbon fuels: hydrogen radical ((H) over dot), methyl radical ((C) over dotH(3)), and ethyl radical ((H) over dotH(2)CH(3)) to investigate the kinetics of their hydrogen abstraction reactions with cyclopentane. The rate constants over a broad temperature range of 150-3000 K are calculated by using the multi-structural variational transition state theory in the small-curvature tunneling approximation (MS-CVT/SCT), by which the multi-structural torsional (MS-T) anharmonicity of partition functions, variational effects, and corner-cutting tunneling are all included in dynamics calculations. We stress the particular importance of considering the MS-T anharmonicity in the rate constant calculation for the reaction with the ethyl radical compared to those with hydrogen and methyl radicals. The MS-T anharmonicity significantly accelerates the reaction with the ethyl radical in the whole temperature range, and in particular, it increases the rate constant by a factor of >-9 at 1000 K. We also found that the tunneling effect drastically increases the rate constants at low-temperatures by up to 3-5 orders of magnitudes. The calculated reaction rate constants have an order of k(H) > k(CH3) > k(CH2CH3).