1
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Selby TM, Goulay F, Soorkia S, Ray A, Jasper AW, Klippenstein SJ, Morozov AN, Mebel AM, Savee JD, Taatjes CA, Osborn DL. Radical-Radical Reactions in Molecular Weight Growth: The Phenyl + Propargyl Reaction. J Phys Chem A 2023; 127:2577-2590. [PMID: 36905386 DOI: 10.1021/acs.jpca.2c08121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
The mechanism for hydrocarbon ring growth in sooting environments is still the subject of considerable debate. The reaction of phenyl radical (C6H5) with propargyl radical (H2CCCH) provides an important prototype for radical-radical ring-growth pathways. We studied this reaction experimentally over the temperature range of 300-1000 K and pressure range of 4-10 Torr using time-resolved multiplexed photoionization mass spectrometry. We detect both the C9H8 and C9H7 + H product channels and report experimental isomer-resolved product branching fractions for the C9H8 product. We compare these experiments to theoretical kinetics predictions from a recently published study augmented by new calculations. These ab initio transition state theory-based master equation calculations employ high-quality potential energy surfaces, conventional transition state theory for the tight transition states, and direct CASPT2-based variable reaction coordinate transition state theory (VRC-TST) for the barrierless channels. At 300 K only the direct adducts from radical-radical addition are observed, with good agreement between experimental and theoretical branching fractions, supporting the VRC-TST calculations of the barrierless entrance channel. As the temperature is increased to 1000 K we observe two additional isomers, including indene, a two-ring polycyclic aromatic hydrocarbon, and a small amount of bimolecular products C9H7 + H. Our calculated branching fractions for the phenyl + propargyl reaction predict significantly less indene than observed experimentally. We present further calculations and experimental evidence that the most likely cause of this discrepancy is the contribution of H atom reactions, both H + indenyl (C9H7) recombination to indene and H-assisted isomerization that converts less stable C9H8 isomers into indene. Especially at low pressures typical of laboratory investigations, H-atom-assisted isomerization needs to be considered. Regardless, the experimental observation of indene demonstrates that the title reaction leads, either directly or indirectly, to the formation of the second ring in polycyclic aromatic hydrocarbons.
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Affiliation(s)
- Talitha M Selby
- Department of Mathematics and Natural Sciences, University of Wisconsin-Milwaukee, West Bend, Wisconsin 53095, United States
| | - Fabien Goulay
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Satchin Soorkia
- Institut des Sciences Moléculaires d'Orsay, Université Paris-Saclay, CNRS, F-91405 Orsay, France
| | - Amelia Ray
- Department of Chemistry, University of Wisconsin-Parkside, Kenosha, Wisconsin 53144, United States
| | - Ahren W Jasper
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Stephen J Klippenstein
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Alexander N Morozov
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - John D Savee
- KLA Corporation, Milpitas, California 95035, United States
| | - Craig A Taatjes
- Combustion Research Facility, Sandia National Laboratories, Mail Stop 9055, Livermore, California 94551, United States
| | - David L Osborn
- Combustion Research Facility, Sandia National Laboratories, Mail Stop 9055, Livermore, California 94551, United States
- Department of Chemical Engineering, University of California, Davis, Davis, California 95616, United States
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2
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Martí C, Michelsen HA, Najm HN, Zádor J. Comprehensive Kinetics on the C 7H 7 Potential Energy Surface under Combustion Conditions. J Phys Chem A 2023; 127:1941-1959. [PMID: 36802584 DOI: 10.1021/acs.jpca.2c08035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2023]
Abstract
The automated kinetics workflow code, KinBot, was used to explore and characterize the regions of the C7H7 potential energy surface that are relevant to combustion environments and especially soot inception. We first explored the lowest-energy region, which includes the benzyl, fulvenallene + H, and cyclopentadienyl + acetylene entry points. We then expanded the model to include two higher-energy entry points, vinylpropargyl + acetylene and vinylacetylene + propargyl. The automated search was able to uncover the pathways from the literature. In addition, three important new routes were discovered: a lower-energy pathway connecting benzyl with vinylcyclopentadienyl, a decomposition mechanism from benzyl that results in side-chain hydrogen atom loss to produce fulvenallene + H, and shorter and lower energy routes to the dimethylene-cyclopentenyl intermediates. We systematically reduced the extended model to a chemically relevant domain composed of 63 wells, 10 bimolecular products, 87 barriers, and 1 barrierless channel and constructed a master equation using the CCSD(T)-F12a/cc-pVTZ//ωB97X-D/6-311++G(d,p) level of theory to provide rate coefficients for chemical modeling. Our calculated rate coefficients show excellent agreement with measured ones. We also simulated concentration profiles and calculated branching fractions from the important entry points to provide an interpretation of this important chemical landscape.
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Affiliation(s)
- Carles Martí
- Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States
| | - Hope A Michelsen
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Habib N Najm
- Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States
| | - Judit Zádor
- Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States
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3
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Zádor J, Martí C, Van de Vijver R, Johansen SL, Yang Y, Michelsen HA, Najm HN. Automated Reaction Kinetics of Gas-Phase Organic Species over Multiwell Potential Energy Surfaces. J Phys Chem A 2023; 127:565-588. [PMID: 36607817 DOI: 10.1021/acs.jpca.2c06558] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Automation of rate-coefficient calculations for gas-phase organic species became possible in recent years and has transformed how we explore these complicated systems computationally. Kinetics workflow tools bring rigor and speed and eliminate a large fraction of manual labor and related error sources. In this paper we give an overview of this quickly evolving field and illustrate, through five detailed examples, the capabilities of our own automated tool, KinBot. We bring examples from combustion and atmospheric chemistry of C-, H-, O-, and N-atom-containing species that are relevant to molecular weight growth and autoxidation processes. The examples shed light on the capabilities of automation and also highlight particular challenges associated with the various chemical systems that need to be addressed in future work.
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Affiliation(s)
- Judit Zádor
- Combustion Research Facility, Sandia National Laboratories, Livermore94550, California, United States
| | - Carles Martí
- Combustion Research Facility, Sandia National Laboratories, Livermore94550, California, United States
| | | | - Sommer L Johansen
- Combustion Research Facility, Sandia National Laboratories, Livermore94550, California, United States
| | - Yoona Yang
- Combustion Research Facility, Sandia National Laboratories, Livermore94550, California, United States
| | - Hope A Michelsen
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder80309, Colorado, United States
| | - Habib N Najm
- Combustion Research Facility, Sandia National Laboratories, Livermore94550, California, United States
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4
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Carpenter BK, Ellison GB, Nimlos MR, Scheer AM. A Conical Intersection Influences the Ground State Rearrangement of Fulvene to Benzene. J Phys Chem A 2022; 126:1429-1447. [PMID: 35191307 DOI: 10.1021/acs.jpca.2c00038] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The rearrangement of fulvene to benzene is believed to play an important role in the formation of soot during hydrocarbon combustion. Previous work has identified two possible mechanisms for the rearrangement─a unimolecular path and a hydrogen-atom-assisted, bimolecular path. Computational results to date have suggested that the unimolecular mechanism faces a barrier of about 74 kcal/mol, which makes it unable to compete with the bimolecular mechanism under typical combustion conditions. This computed barrier is about 10 kcal/mol higher than the experimental value, which is an unusually large discrepancy for modern electronic structure theory. In the present work, we have reinvestigated the unimolecular mechanism computationally, and we have found a second transition state that is approximately 10 kcal/mol lower in energy than the previously identified one and, therefore, in excellent agreement with the experimental value. The existence of two transition states for the same rearrangement arises because there is a conical intersection between the two lowest singlet states which occurs in the vicinity of the reaction coordinates. The two possible paths around the cone on the lower adiabatic surface give rise to the two distinct saddle points. The lower barrier for the unimolecular mechanism now makes it competitive with the bimolecular one, according to our calculations. In support of this conclusion, we have reanalyzed some previous experimental results on anisole pyrolysis, which leads to benzene as a significant product and have shown that the unimolecular and bimolecular mechanisms for fulvene → benzene must be occurring competitively in that system. Finally, we have identified that similar conical intersections arise during the isomerizations of benzofulvene and isobenzofulvene to naphthalene.
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Affiliation(s)
- Barry K Carpenter
- School of Chemistry, Cardiff University, Main Building, Park PL, Cardiff CF10 3AT, U.K
| | - G Barney Ellison
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Mark R Nimlos
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - Adam M Scheer
- Recurve Inc., 4014 South Lemay Avenue, Unit 22, Fort Collins, Colorado 80525, United States
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5
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Zhao L, Prendergast M, Kaiser RI, Xu B, Lu W, Ahmed M, Hasan Howlader A, Wnuk SF, Korotchenko AS, Evseev MM, Bashkirov EK, Azyazov VN, Mebel AM. A molecular beam and computational study on the barrierless gas phase formation of (iso)quinoline in low temperature extraterrestrial environments. Phys Chem Chem Phys 2021; 23:18495-18505. [PMID: 34612388 DOI: 10.1039/d1cp02169a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Despite remarkable progress toward the understanding of the formation pathways leading to polycyclic aromatic hydrocarbons (PAHs) in combustion systems and in deep space, the complex reaction pathways leading to nitrogen-substituted PAHs (NPAHs) at low temperatures of molecular clouds and hydrocarbon-rich, nitrogen-containing atmospheres of planets and their moons like Titan have remained largely obscure. Here, we demonstrate through laboratory experiments and computations that the simplest prototype of NPAHs - quinoline and isoquinoline (C9H7N) - can be synthesized via rapid and de-facto barrier-less reactions involving o-, m- and p-pyridinyl radicals (C5H4N˙) with vinylacetylene (C4H4) under low-temperature conditions.
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Affiliation(s)
- Long Zhao
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA.
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6
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Jin H, Xing L, Yang J, Zhou Z, Qi F, Farooq A. Continuous Butadiyne Addition to Propargyl: A Radical-Efficient Pathway for Polycyclic Aromatic Hydrocarbons. J Phys Chem Lett 2021; 12:8109-8114. [PMID: 34410145 DOI: 10.1021/acs.jpclett.1c02062] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Polycyclic aromatic hydrocarbons (PAHs) play a crucial role in soot inception, interstellar evolution, and nanomaterial synthesis. Although several mechanisms, such as hydrogen-abstraction acetylene/vinylacetylene addition, have previously been proposed, PAH formation and growth are not yet fully understood. We propose an alternate PAH growth mechanism wherein propargyl radical reacts with butadiyne to form larger radicals containing newly fused aromatic rings. Butadiyne is an important intermediate in hydrocarbon oxidation and carbon rich stars, while propargyl is one of the most important resonantly stabilized radicals that persists for long times. Our proposed mechanism is validated by quantum chemical calculations, elementary reaction experiments, laminar flame analysis, and kinetic modeling. Our findings challenge the conventional wisdom that radical site regeneration, being central to PAH growth, requires sequential hydrogen elimination and/or abstraction. In our proposed mechanism, PAH growth does not depend on abundant free radical consumption, and could, therefore, help explain carbonaceous nanoparticle coalescence in radical-deficient reaction environments.
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Affiliation(s)
- Hanfeng Jin
- Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
| | - Lili Xing
- Energy and Power Engineering Institute, Henan University of Science and Technology, Luoyang, Henan 471003, China
| | - Jiuzhong Yang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, China
| | - Zhongyue Zhou
- Key Laboratory for Power Machinery and Engineering of MOE, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Fei Qi
- Key Laboratory for Power Machinery and Engineering of MOE, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Aamir Farooq
- Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
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7
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Caster KL, Selby TM, Osborn DL, Le Picard SD, Goulay F. Product Detection of the CH(X 2Π) Radical Reaction with Cyclopentadiene: A Novel Route to Benzene. J Phys Chem A 2021; 125:6927-6939. [PMID: 34374546 DOI: 10.1021/acs.jpca.1c03517] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reaction of the methylidyne radical (CH(X2Π)) with cyclopentadiene (c-C5H6) is studied in the gas phase at 4 Torr and 373 K using a multiplexed photoionization mass spectrometer. Under multiple collision conditions, the dominant product channel observed is the formation of C6H6 + H. Fitting the photoionization spectrum using reference spectra allows for isomeric resolution of C6H6 isomers, where benzene is the largest contributor with a relative branching fraction of 90 (±5)%. Several other C6H6 isomers are found to have smaller contributions, including fulvene with a branching fraction of 8 (±5)%. Master Equation calculations for four different entrance channels on the C6H7 potential energy surface are performed to explore the competition between CH cycloaddition to a C═C bond vs CH insertion into C-H bonds of cyclopentadiene. Previous studies on CH addition to unsaturated hydrocarbons show little evidence for the C-H insertion pathway. The present computed branching fractions support benzene as the sole cyclic product from CH cycloaddition, whereas fulvene is the dominant product from two of the three pathways for CH insertion into the C-H bonds of cyclopentadiene. The combination of experiment with Master Equation calculations implies that insertion must account for ∼10 (±5)% of the overall CH + cyclopentadiene mechanism.
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Affiliation(s)
- Kacee L Caster
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Talitha M Selby
- Department of Mathematics and Natural Sciences, University of Wisconsin-Milwaukee, West Bend, Wisconsin 53095, United States
| | - David L Osborn
- Combustion Research Facility, Sandia National Laboratories, Mail Stop 9055, Livermore, California 94551, United States
| | - Sebastien D Le Picard
- IPR (Institut de Physique de Rennes), UMR 6251, Univ Rennes, CNRS, F-35000 Rennes, France
| | - Fabien Goulay
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
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8
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Zhang X, Li L, Wu Z, Zhu H, Xie Y, Schaefer HF. Heteroatom (N, P, As, Sb, Bi) Effects on the Resonance-Stabilized 2-, 3-, and 4-Picolyl Radicals. Inorg Chem 2021; 60:5860-5867. [PMID: 33770433 DOI: 10.1021/acs.inorgchem.1c00275] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Important recent experimental studies have allowed the isomer-selective identification of the 2-, 3-, and 4-picolyl radicals. The picolyl radicals and their valence isoelectronic P, As, Sb, and Bi congeners are investigated here. For the three observed parent radicals, the theoretical ionization potentials agree with experiment to within 0.02 eV. Two rules are proposed for predicting vertical ionization potentials (EVIE) and relative energies. The EVIE values for these radicals will be higher when large percentages of the SOMO orbitals are distributed on the atoms with greater electronegativities. The cations of these systems were also studied along with the closed-shell methylpyridines and their P, As, Sb, and Bi analogs. The energies for the cationic species will lie lower when high percentages of π natural localized molecular orbitals occur on the more electronegative atoms. The structures of the 2- and 4-isomers strongly depend upon the heteroatoms, with the C-C linkages adopting a single-double alternating bond manner when the heteroatoms become heavier. The 3-isomers adopt roughly equal C-C bond distances with small changes from N to Bi.
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Affiliation(s)
- Xuewen Zhang
- College of Pharmaceutical Sciences, Institute of Life Science and Green Development, Hebei University, Baoding 071002, China
| | - Longfei Li
- College of Pharmaceutical Sciences, Institute of Life Science and Green Development, Hebei University, Baoding 071002, China
| | - Zeyu Wu
- College of Pharmaceutical Sciences, Institute of Life Science and Green Development, Hebei University, Baoding 071002, China
| | - Huajie Zhu
- College of Pharmaceutical Sciences, Institute of Life Science and Green Development, Hebei University, Baoding 071002, China
| | - Yaoming Xie
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Henry F Schaefer
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602, United States
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9
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He C, Nikolayev AA, Zhao L, Thomas AM, Doddipatla S, Galimova GR, Azyazov VN, Mebel AM, Kaiser RI. Gas-Phase Formation of C 5H 6 Isomers via the Crossed Molecular Beam Reaction of the Methylidyne Radical (CH; X 2Π) with 1,2-Butadiene (CH 3CHCCH 2; X 1A'). J Phys Chem A 2021; 125:126-138. [PMID: 33397109 DOI: 10.1021/acs.jpca.0c08731] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The bimolecular gas-phase reaction of the methylidyne radical (CH; X2Π) with 1,2-butadiene (CH2CCHCH3; X1A') was investigated at a collision energy of 20.6 kJ mol-1 under single collision conditions. Combining our laboratory data with high-level electronic structure calculations, we reveal that this bimolecular reaction proceeds through the barrierless addition of the methylidyne radical to the carbon-carbon double bonds of 1,2-butadiene leading to doublet C5H7 intermediates. These collision adducts undergo a nonstatistical unimolecular decomposition through atomic hydrogen elimination to at least the cyclic 1-vinyl-cyclopropene (p5/p26), 1-methyl-3-methylenecyclopropene (p28), and 1,2-bis(methylene)cyclopropane (p29) in overall exoergic reactions. The barrierless nature of this bimolecular reaction suggests that these cyclic C5H6 isomers might be viable targets to be searched for in cold molecular clouds like TMC-1.
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Affiliation(s)
- Chao He
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | | | - Long Zhao
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Aaron M Thomas
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Srinivas Doddipatla
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Galiya R Galimova
- Samara National Research University, Samara 443086, Russian Federation.,Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Valeriy N Azyazov
- Samara National Research University, Samara 443086, Russian Federation.,Lebedev Physical Institute, Samara 443011, Russian Federation
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
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10
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Kohse-Höinghaus K. Combustion in the future: The importance of chemistry. PROCEEDINGS OF THE COMBUSTION INSTITUTE. INTERNATIONAL SYMPOSIUM ON COMBUSTION 2020; 38:S1540-7489(20)30501-0. [PMID: 33013234 PMCID: PMC7518234 DOI: 10.1016/j.proci.2020.06.375] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Revised: 05/18/2020] [Accepted: 06/28/2020] [Indexed: 06/11/2023]
Abstract
Combustion involves chemical reactions that are often highly exothermic. Combustion systems utilize the energy of chemical compounds released during this reactive process for transportation, to generate electric power, or to provide heat for various applications. Chemistry and combustion are interlinked in several ways. The outcome of a combustion process in terms of its energy and material balance, regarding the delivery of useful work as well as the generation of harmful emissions, depends sensitively on the molecular nature of the respective fuel. The design of efficient, low-emission combustion processes in compliance with air quality and climate goals suggests a closer inspection of the molecular properties and reactions of conventional, bio-derived, and synthetic fuels. Information about flammability, reaction intensity, and potentially hazardous combustion by-products is important also for safety considerations. Moreover, some of the compounds that serve as fuels can assume important roles in chemical energy storage and conversion. Combustion processes can furthermore be used to synthesize materials with attractive properties. A systematic understanding of the combustion behavior thus demands chemical knowledge. Desirable information includes properties of the thermodynamic states before and after the combustion reactions and relevant details about the dynamic processes that occur during the reactive transformations from the fuel and oxidizer to the products under the given boundary conditions. Combustion systems can be described, tailored, and improved by taking chemical knowledge into account. Combining theory, experiment, model development, simulation, and a systematic analysis of uncertainties enables qualitative or even quantitative predictions for many combustion situations of practical relevance. This article can highlight only a few of the numerous investigations on chemical processes for combustion and combustion-related science and applications, with a main focus on gas-phase reaction systems. It attempts to provide a snapshot of recent progress and a guide to exciting opportunities that drive such research beyond fossil combustion.
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Key Words
- 2M2B, 2-methyl-2-butene
- AFM, atomic force microscopy
- ALS, Advanced Light Source
- APCI, atmospheric pressure chemical ionization
- ARAS, atomic resonance absorption spectroscopy
- ATcT, Active Thermochemical Tables
- BC, black carbon
- BEV, battery electric vehicle
- BTL, biomass-to-liquid
- Biofuels
- CA, crank angle
- CCS, carbon capture and storage
- CEAS, cavity-enhanced absorption spectroscopy
- CFD, computational fluid dynamics
- CI, compression ignition
- CRDS, cavity ring-down spectroscopy
- CTL, coal-to-liquid
- Combustion
- Combustion chemistry
- Combustion diagnostics
- Combustion kinetics
- Combustion modeling
- Combustion synthesis
- DBE, di-n-butyl ether
- DCN, derived cetane number
- DEE, diethyl ether
- DFT, density functional theory
- DFWM, degenerate four-wave mixing
- DMC, dimethyl carbonate
- DME, dimethyl ether
- DMM, dimethoxy methane
- DRIFTS, diffuse reflectance infrared Fourier transform spectroscopy
- EGR, exhaust gas recirculation
- EI, electron ionization
- Emissions
- Energy
- Energy conversion
- FC, fuel cell
- FCEV, fuel cell electric vehicle
- FRET, fluorescence resonance energy transfer
- FT, Fischer-Tropsch
- FTIR, Fourier-transform infrared
- Fuels
- GC, gas chromatography
- GHG, greenhouse gas
- GTL, gas-to-liquid
- GW, global warming
- HAB, height above the burner
- HACA, hydrogen abstraction acetylene addition
- HCCI, homogeneous charge compression ignition
- HFO, heavy fuel oil
- HRTEM, high-resolution transmission electron microscopy
- IC, internal combustion
- ICEV, internal combustion engine vehicle
- IE, ionization energy
- IPCC, Intergovernmental Panel on Climate Change
- IR, infrared
- JSR, jet-stirred reactor
- KDE, kernel density estimation
- KHP, ketohydroperoxide
- LCA, lifecycle analysis
- LH2, liquid hydrogen
- LIF, laser-induced fluorescence
- LIGS, laser-induced grating spectroscopy
- LII, laser-induced incandescence
- LNG, liquefied natural gas
- LOHC, liquid organic hydrogen carrier
- LT, low-temperature
- LTC, low-temperature combustion
- MBMS, molecular-beam MS
- MDO, marine diesel oil
- MS, mass spectrometry
- MTO, methanol-to-olefins
- MVK, methyl vinyl ketone
- NOx, nitrogen oxides
- NTC, negative temperature coefficient
- OME, oxymethylene ether
- OTMS, Orbitrap MS
- PACT, predictive automated computational thermochemistry
- PAH, polycyclic aromatic hydrocarbon
- PDF, probability density function
- PEM, polymer electrolyte membrane
- PEPICO, photoelectron photoion coincidence
- PES, photoelectron spectrum/spectra
- PFR, plug-flow reactor
- PI, photoionization
- PIE, photoionization efficiency
- PIV, particle imaging velocimetry
- PLIF, planar laser-induced fluorescence
- PM, particulate matter
- PM10 PM2,5, sampled fractions with sizes up to ∼10 and ∼2,5 µm
- PRF, primary reference fuel
- QCL, quantum cascade laser
- RCCI, reactivity-controlled compression ignition
- RCM, rapid compression machine
- REMPI, resonance-enhanced multi-photon ionization
- RMG, reaction mechanism generator
- RON, research octane number
- Reaction mechanisms
- SI, spark ignition
- SIMS, secondary ion mass spectrometry
- SNG, synthetic natural gas
- SNR, signal-to-noise ratio
- SOA, secondary organic aerosol
- SOEC, solid-oxide electrolysis cell
- SOFC, solid-oxide fuel cell
- SOx, sulfur oxides
- STM, scanning tunneling microscopy
- SVO, straight vegetable oil
- Synthetic fuels
- TDLAS, tunable diode laser absorption spectroscopy
- TOF-MS, time-of-flight MS
- TPES, threshold photoelectron spectrum/spectra
- TPRF, toluene primary reference fuel
- TSI, threshold sooting index
- TiRe-LII, time-resolved LII
- UFP, ultrafine particle
- VOC, volatile organic compound
- VUV, vacuum ultraviolet
- WLTP, Worldwide Harmonized Light Vehicle Test Procedure
- XAS, X-ray absorption spectroscopy
- YSI, yield sooting index
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11
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Reilly NJ, Kokkin DL, Ward ML, Flores J, Ross SD, McCaslin LM, Stanton JF. Gas-Phase Optical Detection of 3-Ethynylcyclopentenyl: A Resonance-Stabilized C7H7 Radical with an Embedded 1-Vinylpropargyl Chromophore. J Am Chem Soc 2020; 142:10400-10411. [DOI: 10.1021/jacs.0c01579] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Neil J. Reilly
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston Massachusetts 02125, United States
| | - Damian L. Kokkin
- Department of Chemistry, Marquette University, P.O. Box 1881 Milwaukee, Wisconsin 53201, United States
| | - Meredith L. Ward
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston Massachusetts 02125, United States
| | - Jonathan Flores
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston Massachusetts 02125, United States
| | - Sederra D. Ross
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston Massachusetts 02125, United States
| | - Laura M. McCaslin
- Institute of Chemistry and the Fritz Haber Center for Molecular Dynamics, The Hebrew University, Jerusalem 9190401, Israel
| | - John F. Stanton
- Quantum Theory Project, Departments of Chemistry and Physics, The University of Florida, Gainesville Florida 32611, United States
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12
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Abstract
New ideas and theoretical results offer a solution to soot particle inception following critical examination of prior proposals.
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Affiliation(s)
- Michael Frenklach
- Department of Mechanical Engineering
- University of California
- Berkeley
- USA
| | - Alexander M. Mebel
- Department of Chemistry and Biochemistry
- Florida International University
- Miami
- USA
- Samara National Research University
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13
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Baroncelli M, Mao Q, Galle S, Hansen N, Pitsch H. Role of ring-enlargement reactions in the formation of aromatic hydrocarbons. Phys Chem Chem Phys 2020; 22:4699-4714. [DOI: 10.1039/c9cp05854k] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ring-enlargement reactions can provide a fast route towards the formation of six-membered single-ring or polycyclic aromatic hydrocarbons (PAHs).
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Affiliation(s)
- Martina Baroncelli
- Institute for Combustion Technology
- RWTH Aachen University
- 52062 Aachen
- Germany
| | - Qian Mao
- Institute for Combustion Technology
- RWTH Aachen University
- 52062 Aachen
- Germany
| | - Simon Galle
- Institute for Combustion Technology
- RWTH Aachen University
- 52062 Aachen
- Germany
| | - Nils Hansen
- Combustion Research Facility, Sandia National Laboratories
- Livermore
- USA
| | - Heinz Pitsch
- Institute for Combustion Technology
- RWTH Aachen University
- 52062 Aachen
- Germany
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14
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Sullivan EN, Nichols B, von Kugelgen S, da Silva G, Neumark DM. Multiphoton dissociation dynamics of the indenyl radical at 248 nm and 193 nm. J Chem Phys 2019; 151:174303. [PMID: 31703498 PMCID: PMC7043848 DOI: 10.1063/1.5121294] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 10/10/2019] [Indexed: 11/14/2022] Open
Abstract
Photofragment translational spectroscopy is used to investigate the unimolecular photodissociation of the indenyl radical (C9H7). C9H7 radicals are generated by photodetachment of C9H7 - anions and are dissociated at 248 nm (5.00 eV) and 193 nm (6.42 eV). The following product channels are definitively observed at both wavelengths: C2H2 + C7H5, C2H2 + C3H3 + C4H2, and C2H2 + C2H2 + C5H3. The three-body product channels are energetically inaccessible from single photon excitation at either dissociation wavelength. This observation, in combination with calculated dissociation rates and laser power studies, implies that all dissociation seen in this experiment occurs exclusively through multiphoton processes in which the initial C9H7 radical absorbs two photons sequentially prior to dissociation to two or three fragments. The corresponding translational energy distributions for each product channel peak well below the maximum available energy for two photons and exhibit similar behavior regardless of dissociation wavelength. These results suggest that all products are formed by internal conversion to the ground electronic state, followed by dissociation.
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Affiliation(s)
- Erin N. Sullivan
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Bethan Nichols
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Stephen von Kugelgen
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Gabriel da Silva
- Department of Chemical Engineering, University of Melbourne, Victoria 3010 Australia
| | - Daniel M. Neumark
- Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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15
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He C, Zhao L, Thomas AM, Galimova GR, Mebel AM, Kaiser RI. A combined experimental and computational study on the reaction dynamics of the 1-propynyl radical (CH 3CC; X 2A 1) with ethylene (H 2CCH 2; X 1A 1g) and the formation of 1-penten-3-yne (CH 2CHCCCH 3; X 1A'). Phys Chem Chem Phys 2019; 21:22308-22319. [PMID: 31576858 DOI: 10.1039/c9cp04073k] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The crossed molecular beam reactions of the 1-propynyl radical (CH3CC; X2A1) with ethylene (H2CCH2; X1A1g) and ethylene-d4 (D2CCD2; X1A1g) were performed at collision energies of 31 kJ mol-1 under single collision conditions. Combining our laboratory data with ab initio electronic structure and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations, we reveal that the reaction is initiated by the barrierless addition of the 1-propynyl radical to the π-electron density of the unsaturated hydrocarbon of ethylene leading to a doublet C5H7 intermediate(s) with a life time(s) longer than the rotation period(s). The reaction eventually produces 1-penten-3-yne (p1) plus a hydrogen atom with an overall reaction exoergicity of 111 ± 16 kJ mol-1. About 35% of p1 originates from the initial collision complex followed by C-H bond rupture via a tight exit transition state located 22 kJ mol-1 above the separated products. The collision complex (i1) can also undergo a [1,2] hydrogen atom shift to the CH3CHCCCH3 intermediate (i2) prior to a hydrogen atom release; RRKM calculations suggest that this pathway contributes to about 65% of p1. In higher density environments such as in combustion flames and circumstellar envelopes of carbon stars close to the central star, 1-penten-3-yne (p1) may eventually form the cyclopentadiene (c-C5H6) isomer via hydrogen atom assisted isomerization followed by hydrogen abstraction to the cyclopentadienyl radical (c-C5H5) as an important pathway to key precursors to polycyclic aromatic hydrocarbons (PAHs) and to carbonaceous nanoparticles.
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Affiliation(s)
- Chao He
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
| | - Long Zhao
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
| | - Aaron M Thomas
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
| | - Galiya R Galimova
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, USA. and Samara National Research University, Samara 443086, Russia
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, USA. and Samara National Research University, Samara 443086, Russia
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, USA.
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16
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Caster KL, Donnellan ZN, Selby TM, Goulay F. Kinetic Investigations of the CH (X2Π) Radical Reaction with Cyclopentadiene. J Phys Chem A 2019; 123:5692-5703. [PMID: 31194547 DOI: 10.1021/acs.jpca.9b03813] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kacee L. Caster
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Zachery N. Donnellan
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
| | - Talitha M. Selby
- Department of Mathematics and Natural Sciences, University of Wisconsin—Milwaukee, West Bend, Wisconsin 53095, United States
| | - F. Goulay
- C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
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17
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Thomas AM, Zhao L, He C, Mebel AM, Kaiser RI. A Combined Experimental and Computational Study on the Reaction Dynamics of the 1-Propynyl (CH3CC)–Acetylene (HCCH) System and the Formation of Methyldiacetylene (CH3CCCCH). J Phys Chem A 2018; 122:6663-6672. [DOI: 10.1021/acs.jpca.8b05530] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Aaron M. Thomas
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | - Long Zhao
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | - Chao He
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
| | - Alexander M. Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Ralf I. Kaiser
- Department of Chemistry, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, United States
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18
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Shapero M, Ramphal IA, Neumark DM. Photodissociation of the Cyclopentadienyl Radical at 248 nm. J Phys Chem A 2018; 122:4265-4272. [DOI: 10.1021/acs.jpca.7b11837] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mark Shapero
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States
| | - Isaac A. Ramphal
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States
| | - Daniel M. Neumark
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States
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19
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Reilly NJ, da Silva G, Wilcox CM, Ge Z, Kokkin DL, Troy TP, Nauta K, Kable SH, McCarthy MC, Schmidt TW. Interconversion of Methyltropyl and Xylyl Radicals: A Pathway Unavailable to the Benzyl–Tropyl Rearrangement. J Phys Chem A 2018; 122:1261-1269. [DOI: 10.1021/acs.jpca.7b11914] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Neil J. Reilly
- Department
of Chemistry, University of Massachusetts Boston, 100 Morrissey
Boulevard, Boston, Massachusetts 02125, United States
| | - Gabriel da Silva
- Department
of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Callan M. Wilcox
- School
of Chemistry, UNSW Sydney, Sydney, New South Wales 2052, Australia
| | - Zijun Ge
- School
of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Damian L. Kokkin
- Department
of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States
| | - Tyler P. Troy
- Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Klaas Nauta
- School
of Chemistry, UNSW Sydney, Sydney, New South Wales 2052, Australia
| | - Scott H. Kable
- School
of Chemistry, UNSW Sydney, Sydney, New South Wales 2052, Australia
| | - Michael C. McCarthy
- Harvard−Smithsonian
Center for Astrophysics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Timothy W. Schmidt
- School
of Chemistry, UNSW Sydney, Sydney, New South Wales 2052, Australia
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20
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da Silva G. Mystery of 1-Vinylpropargyl Formation from Acetylene Addition to the Propargyl Radical: An Open-and-Shut Case. J Phys Chem A 2017; 121:2086-2095. [DOI: 10.1021/acs.jpca.6b12996] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gabriel da Silva
- Department of Chemical and
Biomolecular Engineering, The University of Melbourne, Melbourne, Victoria 3010, Australia
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21
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Constantinidis P, Hirsch F, Fischer I, Dey A, Rijs AM. Products of the Propargyl Self-Reaction at High Temperatures Investigated by IR/UV Ion Dip Spectroscopy. J Phys Chem A 2016; 121:181-191. [DOI: 10.1021/acs.jpca.6b08750] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- P. Constantinidis
- Institute
of Physical and Theoretical Chemistry, University of Würzburg, Am
Hubland, D-97074 Würzburg, Germany
| | - F. Hirsch
- Institute
of Physical and Theoretical Chemistry, University of Würzburg, Am
Hubland, D-97074 Würzburg, Germany
| | - I. Fischer
- Institute
of Physical and Theoretical Chemistry, University of Würzburg, Am
Hubland, D-97074 Würzburg, Germany
| | - A. Dey
- Radboud University, Institute for Molecules and
Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
| | - A. M. Rijs
- Radboud University, Institute for Molecules and
Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
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22
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Buckingham GT, Porterfield JP, Kostko O, Troy TP, Ahmed M, Robichaud DJ, Nimlos MR, Daily JW, Ellison GB. The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical. J Chem Phys 2016; 145:014305. [DOI: 10.1063/1.4954895] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Grant T. Buckingham
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
- National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden Colorado 80401, USA
| | - Jessica P. Porterfield
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
| | - Oleg Kostko
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Tyler P. Troy
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - David J. Robichaud
- National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden Colorado 80401, USA
| | - Mark R. Nimlos
- National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden Colorado 80401, USA
| | - John W. Daily
- Department of Mechanical Engineering, Center for Combustion and Environmental Research, University of Colorado, Boulder, Colorado 80309-0427, USA
| | - G. Barney Ellison
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA
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23
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Thapa J, Spencer M, Akhmedov NG, Goulay F. Kinetics of the OH Radical Reaction with Fulvenallene from 298 to 450 K. J Phys Chem Lett 2015; 6:4997-5001. [PMID: 26625195 DOI: 10.1021/acs.jpclett.5b02417] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Self-recombination and cross-reactions of large resonant stabilized hydrocarbon radicals such as fulvenallenyl (C7H5) are predicted to form polycyclic aromatic hydrocarbons in combustion and the interstellar medium. Although fulvenallenyl is likely to be present in these environments, large uncertainties remain about its formation mechanisms. We have investigated the formation of fulvenallenyl by reacting the OH radical with fulvenallene (C7H6) over the 298 to 450 K temperature range and at a pressure of 5 Torr (667 Pa). The reaction rate coefficient is found to be 8.8(±1.7) × 10(-12) cm(3) s(-1) at room temperature with a negative temperature dependence that can be fit from 298 to 450 K to k(T) = 8.8(±1.7) × 10(-12) (T/298 K)(-6.6(±1.1)) exp[-(8.72(±3.03) kJ mol(-1))/(R((1/T) - (1/298 K)))] cm(3) s(-1). The comparison of the experimental data with calculated abstraction rate coefficients suggests that over the experimental temperature range, association of the OH radical to fulvenallene plays a significant role likely leading to a low fulvenallenyl branching fraction.
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Affiliation(s)
- Juddha Thapa
- Department of Chemistry, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Michael Spencer
- Department of Chemistry, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Novruz G Akhmedov
- Department of Chemistry, West Virginia University , Morgantown, West Virginia 26506, United States
| | - Fabien Goulay
- Department of Chemistry, West Virginia University , Morgantown, West Virginia 26506, United States
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24
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Hemberger P, da Silva G, Trevitt AJ, Gerber T, Bodi A. Are the three hydroxyphenyl radical isomers created equal?--The role of the phenoxy radical. Phys Chem Chem Phys 2015; 17:30076-83. [PMID: 26500055 DOI: 10.1039/c5cp05346c] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated the thermal decomposition of the three hydroxyphenyl radicals (˙C6H4OH) in a heated microtubular reactor. Intermediates and products were identified isomer-selectively applying photoion mass-selected threshold photoelectron spectroscopy with vacuum ultraviolet synchrotron radiation. Similarly to the phenoxy radical (C6H5-O˙), hydroxyphenyl decomposition yields cyclopentadienyl (c-C5H5) radicals in a decarbonylation reaction at elevated temperatures. This finding suggests that all hydroxyphenyl isomers first rearrange to form phenoxy species, which subsequently decarbonylate, a mechanism which we also investigate computationally. Meta- and para-radicals were selectively produced and spectroscopically detectable, whereas the ortho isomer could not be traced due to its fast rethermalization and rapid decomposition in the reactor. A smaller barrier to isomerization to phenoxy was found to be the reason for this observation. Since hydroxyphenyl species may be present under typical sooting conditions in flames, the resonantly stabilized cyclopentadienyl radical adds to the hydrocarbon pool and can contribute to the formation of polycyclic aromatic hydrocarbons, which are precursors in soot formation.
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Affiliation(s)
- P Hemberger
- Molecular Dynamics Group, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
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