Abstract
Accurate fuel combustion modelling is a matter of immense importance to design clean combustors and reduce greenhouse gas emissions and pollutants. In this Brief Communication, we present the effects of internal dynamics of one n-heptane molecule which are controlling chemical kinetics of hydrogen abstraction reactions through multi-pathway reaction dynamics. It is established that the slope of Arrhenius plots dramatically changes in comparison with the harmonic single static pathway approach in the temperature range of 200–3000 K. We apply a combination of the multiple conformation statistical thermodynamic approach and variational transition-state theory (VTST) to obtain dynamic multi-path rate coefficients (kMP-T-VTST and kMP-LH-VTST). Compared with single-path VTST (kSP-H-VTST) results, the thermal reaction rate coefficients obtained from our MP-VTST calculations differ considerably due to the fact that tunnelling and cross-conformational effects in the reactions, and the anharmonic and quasi-harmonic contributions in multiple conformer molecules cannot be ignored or simplified.
Highlights
Numerous experimental, theoretical and computational efforts have been focused on the pyrolysis reactions of alkanes for many decades [1,2,3,4,5]
In order to compare the single- and multi-pathway Habstraction reaction rate coefficients, we have first fully optimised all the conformers of n-heptane molecule, heptyl radicals and transition states of the reactions of R1–R4 using the ωB97X-D/ccpVTZ chemistry model which has been established to provide accurate geometries and electronic energies close to those predicted by CCSD(T)/cc-pVTZ for n-alkanes [15]
In [1] authors estimated the pyrolysis reaction rate coefficients of n-heptane based on single structure harmonic (QSS-H) approximation considering only the lowest energy transition states and the most stable reactant and products
Summary
Theoretical and computational efforts have been focused on the pyrolysis reactions of alkanes for many decades [1,2,3,4,5]. They considered the most stable structure for each reactant, transition states and products involved in reactions R1–R3 but conformational changes in these structures will lead to multiple pathways in all four channels of R1–R4.
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