Formation of benzene in the interstellar medium

Jones, Brant M.; Zhang, Fangtong; Kaiser, Ralf I.; Jamal, Adeel; Mebel, Alexander M.; Cordiner, Martin; Charnley, Steven B.

doi:10.1073/pnas.1012468108

Cited by 153 publications

(202 citation statements)

References 44 publications

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“…37,38 Another recent study implicates 1,3-butadiene in the formation of benzene in the interstellar medium via reaction with the C 2 H radical. 7 Furthermore, the modeling contained in that study concluded that neutral-neutral chemistry is the dominant source of benzene in the Taurus Molecular Cloud (TMC-1). The postulated chemical mechanism relies on CH + C 3 H 6 → 1,3-butadiene + H reaction which is then followed by 1,3-butadiene + C 2 H → c-C 6 H 6 + H. 7 Our results reported here provide the first direct evidence that 1,3-butadiene is the dominant product of the CH + propene reaction, in support of this assumption.…”

Section: Resultsmentioning

confidence: 99%

“…7 Furthermore, the modeling contained in that study concluded that neutral-neutral chemistry is the dominant source of benzene in the Taurus Molecular Cloud (TMC-1). The postulated chemical mechanism relies on CH + C 3 H 6 → 1,3-butadiene + H reaction which is then followed by 1,3-butadiene + C 2 H → c-C 6 H 6 + H. 7 Our results reported here provide the first direct evidence that 1,3-butadiene is the dominant product of the CH + propene reaction, in support of this assumption. Interestingly, the significant branching fraction for production of 1,2-butadiene may warrant further investigation into its role in the chemistry of hydrocarbon-rich environments.…”

Section: Resultsmentioning

confidence: 99%

“…7 In order to accurately model these systems, detailed chemical data are needed in the form of reaction rate coefficients and product branching fractions. Our purpose here is to determine total product branching fractions and provide mechanistic details for the CH (X 2 Π) + propene reaction.…”

Section: Introductionmentioning

confidence: 99%

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Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

et al. 2013

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The CH(X2Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C4H6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C4H6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05), and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to C4H6 (m/z 54) + D and C4H5D (m/z 55) + H, formed at a ratio of 0.4 (m/z 54) to 1.0 (m/z 55). The D elimination channel forms almost exclusively 1,2-butadiene (0.97 ± 0.20) whereas the H elimination channel leads to the formation of deuterated 1,3-butadiene (0.89 ± 0.18) and 1-butyne (0.11 ± 0.02); photoionization spectra of undeuterated species are used in the fitting of the measured m/z 55 (C4H5D) spectrum. The results are generally consistent with a CH cycloaddition mechanism to the C═C bond of propene, forming 1-methylallyl followed by elimination of a H atom via several competing processes. The direct detection of 1,3-butadiene as a reaction product is an important validation of molecular weight growth schemes implicating the CH + propene reaction, for example, those reported recently for the formation of benzene in the interstellar medium ( Jones, B. M. Proc. Natl. Acad. Sci. U.S. A. 2011, 108, 452−457 ABSTRACTThe CH (X 2 Π) + propene reaction is studied in the gas phase at 298 K and 4 Torr (533.3 Pa) using VUV synchrotron photoionization mass spectrometry. The dominant product channel is the formation of C 4 H 6 (m/z 54) + H. By fitting experimental photoionization spectra to measured spectra of known C 4 H 6 isomers, the following relative branching fractions are obtained: 1,3-butadiene (0.63 ± 0.13), 1,2-butadiene (0.25 ± 0.05) and 1-butyne (0.12 ± 0.03) with no detectable contribution from 2-butyne. The CD + propene reaction is also studied and two product channels are observed that correspond to 2011, 108, 452-457).KEYWORDS: radical, gas-phase, photoionization, synchrotron, propene, methylidyne, mass spectrometry. 3 INTRODUCTIONThe highly reactive methylidyne (CH) radical affects the chemistry of energetic gasphase environments including combustion 1-3 , interplanetary atmospheres 4-6 and the interstellar medium. 7 In order to accurately model these systems, detailed chemical data are needed in the form of reaction rate coefficients and product branching fractions. Our purpose here is to determine total product branching fractions and provide mechanistic details for the CH (X 2 Π) + propene reaction. The present work builds on a series of previous product detection studies of the CH radical with small, unsaturated hydrocarbons: acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), allene (C 3 H 4 , CH 2 CCH 2 ) and propyne (C 3 H 4 , CH 3 CCH). 8 Recent works have also investigated the CH reaction with the carbonyl-conta...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

et al. 2013

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“…C 6 H 6 is a precursor of interstellar polycyclic aromatic hydrocarbons (PAHs) and hydrogenated amorphous carbon grains (aromatic/aliphatic mixture) (44)(45)(46). Its structure is representative of the peripheral sites of a PAH.…”

Section: Discussionmentioning

confidence: 99%

Quantum tunneling observed without its characteristic large kinetic isotope effects

Hama

Ueta

Kouchi

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (≳100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system. quantum tunneling | kinetic isotope effect | heterogeneous reactions | reaction dynamics | astrochemistry

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“…One example of a ring formation reaction is the C 2 H + 1,3-butadiene reaction that has been shown, under single collision conditions to form benzene + H at 40% product yield. 4 For the analogous CN + 1,3-butadiene reaction, however, no ring-closure pathways to pyridine are significantly competitive -only traces of pyridine are reported -due to high reaction barriers compared to linear isobaric species. 15 As shown in the next section, CN does rapidly react with aromatic species and is implicated in high order ring-formation mechanisms.…”

Section: Methodsmentioning

confidence: 99%

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

Trevitt

Goulay

2016

Phys. Chem. Chem. Phys.

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For reactive gas-phase environments, including combustion, extraterrestrials atmospheres and our Earth's atmosphere, the availability of quality chemical data is essential for predictive chemical models. These data include reaction rate coefficients and product branching fractions. This perspective overviews recent isomerresolved production detection experiments for reactions of two of the most reactive gas phase radicals, the CN and CH radicals, with a suite of small hydrocarbons. A particular focus is given to flow-tube experiments using synchrotron photoionization mass spectrometry. Coupled with computational studies and other experiment techniques, flow tube isomer-resolved product detection have provided significant mechanistic details of these radical + neutral reactions with some general patterns emerging. Disciplines Medicine and Health Sciences | Social and Behavioral Sciences ABSTRACTFor reactive gas-phase environments, including combustion, extraterrestrials atmospheres and our Earth's atmosphere, the availability of quality chemical data is essential for predictive chemical models. These data include reaction rate coefficients and product branching fractions. This perspective overviews recent isomer-resolved production detection experiments for reactions of two of the most reactive gas phase radicals, the CN and CH radicals, with a suite of small hydrocarbons. A particular focus is given to flowtube experiments using synchrotron photoionization mass spectrometry. Coupled with computational studies and other experiment techniques, flow tube isomer-resolved product detection have provided significant mechanistic details of these radical + neutral reactions with some general patterns emerging.

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Formation of benzene in the interstellar medium

Cited by 153 publications

References 44 publications

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

Quantum tunneling observed without its characteristic large kinetic isotope effects

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

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