Abstract
The present study complements our previous studies of the reactions of hydrogen atoms with C5 alkene species including 1- and 2-pentene and the branched isomers (2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene), by studying the reactions of hydrogen atoms with C2–C4 alkenes (ethylene, propene, 1- and 2-butene, and isobutene). The aim of the current work is to develop a hierarchical set of rate constants for Ḣ atom addition reactions to C2–C5 alkenes, both linear and branched, which can be used in the development of chemical kinetic models. High-pressure limiting and pressure-dependent rate constants are calculated using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory and a one-dimensional master equation (ME). Rate constant recommendations for Ḣ atom addition and abstraction reactions in addition to alkyl radical decomposition reactions are also proposed and provide a useful tool for use in mechanisms of larger alkenes for which calculations do not exist. Additionally, validation of our theoretical results with single-pulse shock-tube pyrolysis experiments is carried out. An improvement in species mole fraction predictions for alkene pyrolysis is observed, showing the relevance of the present study.
Highlights
Alkenes are important intermediates formed during the oxidation and pyrolysis of larger alkanes and are key components of hydrocarbon fuels
There have been a studies of Ḣ atoms with C2−C4 alkenes.[6−19] This study aims to complement these by providing a comprehensive hierarchical set of rate constants for Ḣ atom addition and abstraction potential energy surfaces (PESs), including their chemically activated pathways for C2−
As described in our previous study of the pentene isomers,[5] test computations implied that the high-pressure limiting rate constant for external Ḣ atom addition to 2M1B was overestimated by a factor of 2−3, which is in line with the variational effect observed by Jasper and Hansen[62] for Ḣ atom addition to highmolecular-weight species
Summary
Alkenes are important intermediates formed during the oxidation and pyrolysis of larger alkanes and are key components of hydrocarbon fuels. An understanding of their combustion chemistry is important in our understanding of hydrocarbon fuel combustion. There have been a studies of Ḣ atoms with C2−C4 alkenes.[6−19] This study aims to complement these by providing a comprehensive hierarchical set of rate constants for Ḣ atom addition and abstraction potential energy surfaces (PESs), including their chemically activated pathways for C2−. By C2−C5 alkenes + Ḣ having atoms calculated at the same level of theory, our results help constrain available models and the development of recommended rate constants, which provide a tool for use in mechanisms of larger alkenes for which calculations do not exist in the literature. Matsugi[19] performed direct trajectory calculations on Ċ 2H5 radical dissociation and discovered a reaction pathway that edvdxiiinsrpesylocaltcnliya(atCtieeȯl2inHmto3ifn)oCart2reHatsdh2Hiec+a2ulfsHnr.oė .mxTpTheChecė 2tyHerde5sl,syuulgelgstaliedonsiwgtngthCHtaȯ 2̇ tHtath3thoeimsrfaomdrfmiaocyaarmltsiboaentcioaaonnnf previously observed in photodissociation experiments radicals.[20,21] Barker et al.[10] studied the reaction of Ḣ +
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