Effect of Hydrogen Bonding Interaction on Kinetics of Cyclopentanol Reaction With Hydroperoxyl Radical at Atmospheric and Combustion Temperatures: A Theoretical Study

The reaction kinetics of hydrogen abstractions from cyclopentanol by hydroperoxyl radical have been comprehensively studied using multistructural canonical variational transition state theory with small curvature tunneling approximation (MS-T-CVT/SCT). The barrier heights and reaction energies have been calculated at the CCSD(T)/cc-pVDZ and CCSD(T)/cc-pVTZ levels of theory with basis set corrections from MP2/cc-pVnZ (where n = D, T, and Q), based on the geometries optimized with the M06-2X/6-311+G(2df,2p) method. The rate coefficients of different hydrogen abstraction sites (α-carbon, β-carbon, γ-carbon, and OH) have been calculated by direct dynamics based on M08-HX/jun-cc-pVTZ electronic structure calculations, as this model chemistry shows the lowest averaged mean unsigned error relative to the benchmark CCSD(T) method. The reaction barrier heights for hydrogen abstraction from various sites follow the order of α-carbon < γ-carbon < β-carbon < OH and follow the order of C─H and O─H bond dissociation energies. Kinetic results suggest that the multistructural torsional anharmonicity, tunneling, and hydrogen bonding interaction are important influential factors for calculating accurate rate coefficients and branching ratios. Hydrogen abstraction reaction from α-carbon site shows the largest contribution to the overall rate coefficients below 1100 K, beyond which hydrogen abstraction reactions from β-carbon and γ-carbon sites become dominant. Hydrogen bonding interaction involved in the transition states significantly reduces the reaction barrier heights and accelerates the single-structural rate coefficients at lower temperatures, but has only a marginal impact on the overall and site-specific MS-T-CVT/SCT rate coefficients, except for the hydrogen abstraction reaction from β-carbon site. However, hydrogen bonding interaction influences the MS-T-CVT/SCT branching ratios. The thermodynamic properties of cyclopentanol and four derived fuel radicals are calculated using the atomization method together with the multistructural partition functions. The simulated auto-ignition reactivity of cyclopentanol/air mixtures is sensitive to the newly calculated rate coefficients and thermodynamic parameters, especially at low temperatures.