<scp>OH</scp>+ Isoprene: A Direct Dynamics Study

Jeon, Jihye; Barker, John R.; Song, Kihyung

doi:10.1002/bkcs.11145

Cited by 4 publications

(5 citation statements)

References 49 publications

(97 reference statements)

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“…Using computational approaches, addition of OH to the tertiary and secondary carbon centers of isoprene have been estimated to be 4–8% of the total OH reactivity. − There is, however, little laboratory evidence to provide any constraint on these branching fractions . If these channels are as significant as calculated, then describing their products is essential.…”

Section: The Challenges That Remainmentioning

confidence: 99%

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Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

et al. 2018

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Isoprene carries approximately half of the flux of non-methane volatile organic carbon emitted to the atmosphere by the biosphere. Accurate representation of its oxidation rate and products is essential for quantifying its influence on the abundance of the hydroxyl radical (OH), nitrogen oxide free radicals (NO ), ozone (O), and, via the formation of highly oxygenated compounds, aerosol. We present a review of recent laboratory and theoretical studies of the oxidation pathways of isoprene initiated by addition of OH, O, the nitrate radical (NO), and the chlorine atom. From this review, a recommendation for a nearly complete gas-phase oxidation mechanism of isoprene and its major products is developed. The mechanism is compiled with the aims of providing an accurate representation of the flow of carbon while allowing quantification of the impact of isoprene emissions on HO and NO free radical concentrations and of the yields of products known to be involved in condensed-phase processes. Finally, a simplified (reduced) mechanism is developed for use in chemical transport models that retains the essential chemistry required to accurately simulate isoprene oxidation under conditions where it occurs in the atmosphere-above forested regions remote from large NO emissions.

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Section: The Challenges That Remainmentioning

confidence: 99%

“…Despite the allylic resonance, abstraction of the methyl hydrogen is likely less than 1% of the total reaction under atmospheric conditions (cf. recent calculations on propene 96 and isoprene 97 ).…”

Section: Location Of Oh Additionmentioning

confidence: 99%

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

et al. 2018

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“…Therefore, in principle, the reaction of isoprene with • OH, NO 3 , O 3 , and • Cl can proceed via both H-abstraction and addition pathways. It has previously been shown that the addition pathway is exclusive for reactions of isoprene with NO 3 and O 3 . ,,, The addition pathway is also the major reaction route for the • OH + isoprene reaction, where H-abstraction from the −CH 3 group to form allylic radicals only plays a minor role (≤1%). ,, However, the H-abstraction pathway has a significantly higher contribution to the removal of isoprene (13–17%) in the reaction of • Cl with isoprene, ,− compared with the reactions of isoprene with • OH, NO 3 , and O 3 . In some locations such as North China Plains or coastal regions, the concentration of • Cl can reach 10% of that of • OH. ,− This implies that the H-abstraction pathway can contribute up to 3.6–4.9% (see the SI) to the total removal of isoprene at daytime even though the only contribution of • Cl on H-abstraction is considered.…”

Section: Introductionmentioning

confidence: 99%

“…7,10,15,16 The addition pathway is also the major reaction route for the • OH + isoprene reaction, where H-abstraction from the −CH 3 group to form allylic radicals only plays a minor role (≤1%). 7,17,18 However, the Habstraction pathway has a significantly higher contribution to the removal of isoprene (13−17%) in the reaction of • Cl with isoprene, 4,19−23 compared with the reactions of isoprene with • OH, NO 3 , and O 3 . In some locations such as North China Plains or coastal regions, the concentration of • Cl can reach 10% of that of • OH.…”

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confidence: 99%

Atmospheric Chemistry of Allylic Radicals from Isoprene: A Successive Cyclization-Driven Autoxidation Mechanism

Guo

Xia

et al. 2021

Environ. Sci. Technol.

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The atmospheric chemistry of isoprene has broad implications for regional air quality and the global climate. Allylic radicals, taking 13−17% yield in the isoprene oxidation by • Cl, can contribute as much as 3.6−4.9% to all possible formed intermediates in local regions at daytime. Considering the large quantity of isoprene emission, the chemistry of the allylic radicals is therefore highly desirable. Here, we investigated the atmospheric oxidation mechanism of the allylic radicals using quantum chemical calculations and kinetics modeling. The results indicate that the allylic radicals can barrierlessly combine with O 2 to form peroxy radicals (RO 2• ). Under ≤100 ppt NO and ≤50 ppt HO 2• conditions, the formed RO 2 • mainly undergo two times "successive cyclization and O 2 addition" to finally form the product fragments 2-alkoxy-acetaldehyde (C 2 H 3 O 2• ) and 3-hydroperoxy-2-oxopropanal (C 3 H 4 O 4 ). The presented reaction illustrates a novel successive cyclization-driven autoxidation mechanism. The formed 3-hydroperoxy-2-oxopropanal product is a new isomer of the atmospheric C 3 H 4 O 4 family and a potential aqueous-phase secondary organic aerosol precursor. Under >100 ppt NO condition, NO can mediate the cyclization-driven autoxidation process to form C 5 H 7 NO 3 , C 5 H 7 NO 7 , and alkoxy radical-related products. The proposed novel autoxidation mechanism advances our current understanding of the atmospheric chemistry of both isoprene and RO 2• .

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“…Oxidation of isoprene by the hydroxyl radical, the latter of which is often referred to as a detergent of the atmosphere because it is the primary agent for removal of atmospheric volatile organic compounds (VOCs), − initiates a series of reactions that results in tropospheric ozone formation and • OH propagation. The oxidation of isoprene in particular involves • OH addition to one of the four sp 2 hybridized carbon centers along the butadiene backbone. , Hydrogen (H) abstraction by • OH is a higher barrier reaction than OH–VOC adduct formation for unsaturated VOCs, − though abstraction pathways have been suggested for several substituted allylic species to occur from nearly atmospheric to combustion-like temperatures, as well as very low pressures. − …”

Section: Introductionmentioning

confidence: 99%

Emerging Nonvalence Anion States of [Isoprene-H·]·H₂O Accessed via Detachment of OH^–·Isoprene

et al. 2020

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The anion photoelectron imaging spectra of an ion with m/z 85, generated under ion source conditions that optimize •OH production in a coexpansion with isoprene, are presented and analyzed with supporting calculations. A spectroscopic feature observed at a vertical electron detachment energy of 2.45 eV, which dominates the photoelectron spectrum measured at 3.495 eV photon energy, is consistent with the OH–·isoprene ion–molecule complex, while additional signal observed at lower electron binding energy can be attributed to other constitutional isomers. However, spectra measured over a 2.2–2.6 eV photon energy range, i.e., from near threshold of the predominant OH–·isoprene detachment feature through the vertical detachment energy, exhibit sharp features with common electron kinetic energies, suggesting autodetachment from a temporary anion prepared by photoexcitation. The photon energy independence of the electron kinetic energy of these features along with the low dipole moment predicted for the neutral •OH·isoprene van der Waals complex, suggest a complex photon-driven process. We present calculations supporting a hypothesis that near-threshold production of the •OH···isoprene reactive complex results in hydrogen abstraction of the isoprene molecule. The newly formed activated complex anion supports a dipole bound state that temporarily traps the near zero-kinetic energy electron and then autodetaches, encoding the low-frequency modes of the dehydrogenated neutral isoprene radical in the electron kinetic energies.

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OH+ Isoprene: A Direct Dynamics Study

Cited by 4 publications

References 49 publications

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

Atmospheric Chemistry of Allylic Radicals from Isoprene: A Successive Cyclization-Driven Autoxidation Mechanism

Emerging Nonvalence Anion States of [Isoprene-H·]·H₂O Accessed via Detachment of OH^–·Isoprene

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OH+ Isoprene: A Direct Dynamics Study

Cited by 4 publications

References 49 publications

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

Atmospheric Chemistry of Allylic Radicals from Isoprene: A Successive Cyclization-Driven Autoxidation Mechanism

Emerging Nonvalence Anion States of [Isoprene-H·]·H2O Accessed via Detachment of OH–·Isoprene

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Emerging Nonvalence Anion States of [Isoprene-H·]·H₂O Accessed via Detachment of OH^–·Isoprene