Theoretical analysis and kinetic modeling on hydrogen addition and abstraction by H radical of 1,3-cyclopentadiene and the associated chain-branching reactions

TL;DR

This study provides a comprehensive theoretical and kinetic analysis of hydrogen addition and abstraction reactions involving cyclopentadiene, revealing key reaction pathways, rate constants, and their implications for combustion modeling.

Contribution

It offers new high-level ab initio data, kinetic rate constants, and insights into reaction mechanisms, including the role of open-chain intermediates, for hydrogen reactions with cyclopentadiene.

Findings

Hydrogen abstraction from saturated carbon in CPD is dominant.

Open-chain intermediates play a significant role in reaction kinetics.

Transformation to straight-chain C5H7 is kinetically unfavorable.

Abstract

Cyclopentadiene (CPD) is an important intermediate in the combustion of fuel and the formation of aromatics. In the present study, the kinetics and thermodynamic properties for hydrogen abstraction and addition with CPD, and the related reactions including the isomerization and decomposition on the C5H7 potential energy surface were systematically investigated by theoretical calculations. High-level ab initio calculations were adopted to obtain the stationary points on the potential energy surfaces of CPD + H. Phenomenological rate coefficients for temperature- and pressure-dependent reactions in the full potential energy surface were calculated by solving the time-dependent multiple-well RRKM/master equation, and the hydrogen abstraction reactions were based on the conventional transition state theory. In terms of the hydrogen abstraction reactions, the hydrogen abstraction from the saturated carbon atom in CPD is found to be the dominant channel. For the hydrogen addition and the associated reactions on the C5H7 PES, the allylic and vinylic cyclopentenyl radicals and C2H2 + C3H5 were found to be the most important channels and reactivity-promoting products, respectively. The previously neglected role of open-chain intermediates in the evaluation of the reaction kinetics has been suggested and the corresponding rate constants have been recommended for inclusion in the modeling of the H+ c-C5H6 reaction. Results indicate that the transformation from to straight-chain C5H7 is kinetically unfavorable due to the high strain energy of the 3-membered ring structure of the isomerization transition state. Moreover, the thermodynamic data and the calculated rate coefficients for both H atom abstraction and addition were incorporated into the kinetics model to examine the impact of the computed pressure-dependent kinetics of C5H6 + H reactions on model predictions.