Theoretical Study of the Reaction of Hydrogen Atoms with Three Pentene Isomers: 2-Methyl-1-butene, 2-Methyl-2-butene, and 3-Methyl-1-butene.

Abstract

This paper presents a comprehensive potential energy surface (PES) for hydrogen atom addition to and abstraction from 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene and the subsequent ß-scission and H atom transfer reactions. Thermochemical parameters for species on the Ċ5H11 potential energy surface (PES) were calculated as a function of temperature (298-2000 K), using a series of isodesmic reactions to determine the formation enthalpies. High-pressure limiting and pressure-dependent rate constants were calculated using Rice-Ramsperger-Kassel-Marcus theory with a one-dimensional master equation. A number of studies have highlighted the fact that C5 intermediate species play a role in polyaromatic hydrocarbon formation and that a fuel's chemical structure can be key in understanding the intermediate species formed during fuel decomposition. Rate constant recommendations for both Ḣ atom addition to, and H-atom abstraction by Ḣ atoms from, linear and branched alkenes have subsequently been proposed by incorporating our earlier work on 1- and 2-pentene, and these can be used in mechanisms of larger alkenes for which calculations do not exist. The current set of rate constants for the reactions of Ḣ atoms with both linear and branched C5 alkenes, including their chemically activated pathways, are the first available in the literature of any reasonable fidelity for combustion modeling and are important for gasoline mechanisms. Validation of our theoretical results with pyrolysis experiments of 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene at 2 bar in a single pulse shock tube (SPST) were carried out, with satisfactory agreement observed.