H- and D-atom formation from the pyrolysis of C6H5CH2Br and C6H5CD2Br: Implications for high-temperature benzyl decomposition

Sivaramakrishnan, R.; Su, M.‐C.; Michael, J.V.

doi:10.1016/j.proci.2010.06.133

Cited by 22 publications

(70 citation statements)

References 26 publications

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“…Dotted lines show the confidence limit of the calculated branching ratios corresponding to a deviation of a factor of 2 in the rate coefficients. lately called into question by the isotope experiments of Sivaramakrishnan et al 31 and Lemieux. 38 In fact, considering this mechanism one cannot explain how the H atom lost by benzyl can originate both from the side chain and the ring portion.…”

Section: ■ Resultsmentioning

confidence: 99%

“…However, in spite of the significant improvement over the original model, still some aspects of the reaction mechanism remain unclear. In particular isotope substitution experiments performed both by Sivaramakrishnan et al 31 and more recently by Lemieux 38 suggest that the hydrogen produced can come from the aromatic ring and also from the side chain. The latter feature cannot be explained by the model in ref 35. Thus, we decided to investigate again benzyl chemical reactivity adopting well tempered metadynamics (WT-MTD) combined with ab initio molecular dynamics, with the purpose of addressing the remaining open questions on its decomposition mechanism, and more in general demonstrate the potential that metadynamics can have in the study of combustion kinetics.…”

Section: ■ Introductionmentioning

confidence: 98%

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Combustion Chemistry via Metadynamics: Benzyl Decomposition Revisited

Polino

Parrinello

2015

J. Phys. Chem. A

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Large polycyclic aromatic hydrocarbons (PAHs) are thought to be responsible for the formation of soot particles in combustion processes. However, there are still uncertainties on the course that leads small molecules to form PAHs. This is largely due to the high number of reactions and intermediates involved. Metadynamics combined with ab initio molecular dynamics can provide a very precious contribution because offers the possibility to explore new possible pathways and suggest new mechanisms. Here, we adopt this method to investigate the chemical evolution of the benzyl radical, whose role is very important in PAHs growth. This species has been intensely studied, and though most of its chemistry is known, there are still open questions regarding its decomposition. The simulation reproduces the most commonly accepted decomposition pathway and it suggests also a new one which can explain recent experimental data that are in contradiction with the old mechanism. In addition, quantitative free energy evaluation of some key reaction steps sheds light on the role of entropy.

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Section: ■ Resultsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 98%

Combustion Chemistry via Metadynamics: Benzyl Decomposition Revisited

Polino

Parrinello

2015

J. Phys. Chem. A

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“…We conclude this paper with a reconsideration of the pathways for the thermal fragmentation of benzyl radical based on all experimental findings. 7,8,13,[48][49][50][51][52][53] The pyrolysis of the benzyl radical is a complex problem. None of the early experimental papers [53][54][55][56][57][58] describing the pyrolysis of C 6 H 5 CH 2 were able to identify any of the thermal fragments except for the H atoms detected by ARAS.…”

Section: Discussionmentioning

confidence: 99%

“…In the early literature, the interconversion of benzyl to tropyl (C 6 H 5 CH 2 C 7 H 7 ) was considered by several groups. [9][10][11][12][13][14][15] However, all recent theoretical studies [16][17][18] find no pathways below 2000 K for the isomerization of benzyl to tropyl. A photoionization search for the isomerization of the C 6 H 5 CD 2 benzyl radical to the C 7 H 5 D 2 tropyl radical with tunable VUV radiation found no evidence for tropyl radical formation.…”

Section: Introductionmentioning

confidence: 99%

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

Buckingham

Porterfield

Kostko

et al. 2016

The Journal of Chemical Physics

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Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 (13)CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 (13)CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).

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“…32 Subsequent shock tube studies performed with HARAS determined that H loss is the dominant dissociation channel with 0.8 H atoms produced per benzyl radical dissociated. 33,34 Deuterated shock tube studies suggested three possible benzyl decay mechanisms: H loss from the ring, H loss from the side chain, and a non-atom loss channel, required to account for the rest of the signal decay. 34 A new technique for investigating the thermal decomposition of radicals was recently presented by Lemieux 35 and Buckingham et al 36 A benzyl radical precursor is passed through a heated microreactor, resulting in radical formation followed by dissociation.…”

Section: Introductionmentioning

confidence: 99%

Benzyl Radical Photodissociation Dynamics at 248 nm

et al. 2015

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The photodissociation of jet cooled benzyl radicals, C7H7, at 248 nm has been studied using photofragment translational spectroscopy. Two dissociation channels were observed, H + C7H6 and CH3 + C6H4. The translational energy distribution determined for each channel suggests that both dissociation mechanisms occur via internal conversion to the ground state followed by intramolecular vibrational redistribution and dissociation. The branching ratio between these two channels has been measured to be (CH3 + C6H4)/(H + C7H6) = 0.011 ± 0.004. The dominance of the H + C7H6 channel is corroborated by the branching ratio calculated using Rice-Ramsperger-Kassel-Marcus theory.

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H- and D-atom formation from the pyrolysis of C6H5CH2Br and C6H5CD2Br: Implications for high-temperature benzyl decomposition

Cited by 22 publications

References 26 publications

Combustion Chemistry via Metadynamics: Benzyl Decomposition Revisited

Combustion Chemistry via Metadynamics: Benzyl Decomposition Revisited

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

Benzyl Radical Photodissociation Dynamics at 248 nm

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