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Li W, Wu M, Wang C, Huang J, Yang J, Xu M, Zhang F, Yang T, Zhao L. Unconventional pathway for the gas-phase formation of 14π-PAHs via self-reaction of the resonantly stabilized radical fulvenallenyl (C 7H 5˙). Chem Sci 2025; 16:7864-7875. [PMID: 40181816 PMCID: PMC11963888 DOI: 10.1039/d5sc00160a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2025] [Accepted: 03/06/2025] [Indexed: 04/05/2025] Open
Abstract
Resonantly stabilized free radicals (RSFRs) are contemplated to be the reactive intermediates in molecular mass-growth processes leading to polycyclic aromatic hydrocarbons (PAHs), which are prevalent in deep space and on Earth. The self-reaction routes of two RSFRs have been recognized as fundamental but more-efficient pathways to form fused benzenoid rings. The present experiment, which exploits a chemical microreactor in combination with an isomer-selective identification technique through fragment-free photoionization utilizing a tunable vacuum ultraviolet (VUV) light in tandem with the detection of the ionized molecules by a high-resolution reflection time-of-flight mass spectrometer (Re-TOF-MS), provides compelling evidence for the formation of phenanthrene and a minor amount of anthracene in the presence of fulvenallenyl (C7H5˙). Further theoretical calculations of the potential energy surfaces of C14H10 and C14H11 reveal that phenanthrene and anthracene can be efficiently produced via a hydrogen-assisted multi-step mechanism [C7H5˙ + C7H5˙ → i3, i3 = (3,4-di(cyclopenta-2,4-dien-1-ylidene)cyclobut-1-ene); i3 + H → phenanthrene + H/anthracene + H or i3 + H → i8 + H → phenanthrene + H/anthracene + H, i8 = (1-(cyclopenta-2,4-dien-1-ylidene)indene)] at low pressures, rather than through the one-step recombination-isomerization of fulvenallenyl radicals. This study provides a novel growth mechanism for tricyclic PAHs, especially in hydrogen-rich environments such as combustion and interstellar environments, which advances the knowledge of PAH propagation and even the formation mechanisms of carbonaceous nanoparticles in our universe.
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Affiliation(s)
- Wang Li
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Mengqi Wu
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China Hefei Anhui 230026 China
| | - Changyang Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Jiabin Huang
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China Hefei Anhui 230026 China
| | - Jiuzhong Yang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Minggao Xu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Feng Zhang
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China Hefei Anhui 230026 China
- Hefei National Laboratory, University of Science and Technology of China Hefei Anhui 230088 China
| | - Tao Yang
- State Key Laboratory of Precision Spectroscopy, East China Normal University Shanghai 200062 China
- Xinjiang Astronomical Observatory, Chinese Academy of Sciences 150 Science 1-Street Urumqi Xinjiang 830011 China
- Collaborative Innovation Center of Extreme Optics, Shanxi University Taiyuan Shanxi 030006 China
| | - Long Zhao
- School of Nuclear Science and Technology, University of Science and Technology of China Hefei Anhui 230027 China
- Deep Space Exploration Laboratory, University of Science and Technology of China Hefei Anhui 230026 China
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Medvedkov IA, Yang Z, Goettl SJ, Kaiser RI. Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C 2; X 1Σ g+/a 3Π u) with 2-Methyl-1,3-butadiene (C 5H 8; X 1A'). J Phys Chem A 2025; 129:3280-3288. [PMID: 40153537 DOI: 10.1021/acs.jpca.5c00639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2025]
Abstract
The crossed molecular beam technique was utilized to explore the reaction of dicarbon C2 (X1Σg+/a3Πu) with 2-methyl-1,3-butadiene (isoprene, CH2C(CH3)CHCH2; X1A') at a collision energy of 28 ± 1 kJ mol-1 using a supersonic dicarbon beam generated via photolysis (248 nm) of helium-seeded tetrachloroethylene (C2Cl4). Experimental data combined with previous ab initio calculations provide evidence of the detection of the hitherto elusive methyl elimination channels leading to acyclic resonantly stabilized hexatetraenyl radicals: 1,2,4,5-hexatetraen-3-yl (CH2CC•CHCCH2) and/or 1,3,4,5-hexatetraen-3-yl (CH2CHC•CCCH2). These pathways are exclusive to the singlet potential energy surface, with the reaction initiated by the barrierless addition of a dicarbon to one of the carbon-carbon double bonds in the diene. In combustion systems, both hexatetraenyl radicals can isomerize to the phenyl radical (C6H5) through a hydrogen atom-assisted isomerization─the crucial reaction intermediate and molecular mass growth species step toward the formation of polycyclic aromatic hydrocarbons and soot.
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Affiliation(s)
- Iakov A Medvedkov
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Zhenghai Yang
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Shane J Goettl
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
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Zhang J, Gao J, Wang H, Guan J, Xu G, Xing L, Truhlar DG, Wang Z. Less-Dominant Resonance Configuration of Propargyl Radical Leads to a Growth Mechanism for Polycyclic Aromatic Hydrocarbons that Preserves the Cyclopenta Ring. J Am Chem Soc 2025; 147:9283-9293. [PMID: 40043144 DOI: 10.1021/jacs.4c15155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2025]
Abstract
Understanding the growth of polycyclic aromatic hydrocarbons (PAHs) is essential for combustion, astrochemistry, and carbon-based nanomaterial synthesis. This study presents theory-guided experiments on radical-radical combination reactions of propargyl (•C3H3). The addition of •C3H3 to three cyclopenta-fused PAH radicals─1-indenyl (•1-C9H7), acenaphthenyl (•C12H9), and 4H-cyclopenta[def]phenanthrenyl (•C15H9)─revealed that the reaction between the dominant propyne-3-yl resonance configuration of •C3H3 and the three radicals consistently produces PAHs with all hexagonal rings, while the reaction between the less dominant allene-1-yl resonance configuration of •C3H3 and the three radicals selectively preserves the cyclopenta ring and forms a new hexagonal ring. Elusive intermediates and isomeric products were observed and identified by combining molecular beam-sampling synchrotron photoionization mass spectrometry with gas chromatography-mass spectrometry. The complementary results suggest a high selectivity of the allene-1-yl addition pathway, which is thermodynamically controlled. The findings presented here are based on a combination of experimental capabilities, and they provide new mechanisms and insights into the selective formation of bowl-shaped PAHs, serving as templates for fullerene and nanotube structures. The high selectivity of the allene-1-yl pathway provides a rational synthetic strategy for cyclopenta-fused PAHs, bearing barrierless and facile radical-radical reaction pathways in various environments, including high-temperature combustion, circumstellar envelopes, and cold molecular clouds.
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Affiliation(s)
- Jinyang Zhang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Jiao Gao
- School of Pharmacy, Anhui Medical College, Hefei, Anhui 230601, P. R. China
| | - Hong Wang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Jiwen Guan
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Guangxian Xu
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
| | - Lili Xing
- Energy and Power Engineering Institute, Henan University of Science and Technology, Luoyang, Henan 471003, P. R. China
| | - Donald G Truhlar
- Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, United States
| | - Zhandong Wang
- National Synchrotron Radiation Laboratory, and State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
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Trang HTT, Thuong NT, Pham TV. Investigation of product formation in the H + H 2C = C = CH reaction: a comparison of experimental and theoretical kinetics. J Mol Model 2025; 31:110. [PMID: 40056283 DOI: 10.1007/s00894-025-06325-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2024] [Accepted: 02/13/2025] [Indexed: 03/10/2025]
Abstract
CONTEXT The H2CCCH radical plays a crucial role in combustion chemistry, astrophysical processes, and the formation of complex organic molecules, serving as a key intermediate in the synthesis of polycyclic aromatic hydrocarbons and soot precursors. The reactions of H2CCCH with small species are significant for understanding the mechanisms of hydrocarbon transformation in combustion, atmospheric chemistry, and interstellar environments. In the present study, the mechanism and kinetics of the H + H2CCCH have been thoroughly characterized. The calculated results indicate that the reaction can proceed via H-addition to the H2CCCH carbon chain without an energy barrier, forming the adducts (C3H4). These intermediates can then undergo H2-abstraction or carbon-chain cleavage to create various products, in which PR1 (1HCCCH + H2) and PR4 (H2CCC + H2) are the main products of the reaction system. Furthermore, the triplet potential surface shows the dominant channel forming the product PR11 (3HCCCH + H2). In the low-temperature region, PR4 is dominant, exhibiting a 70% branching ratio at 400 K; at higher temperatures, the PR11 product prevails, with a 65.7% branching ratio at 2000 K. The bimolecular rate constants of the reaction are positively dependent on temperatures but negatively dependent on pressures. The calculated rate constants in this study agree well with the available literature data. The computational results of the H + H2CCCH reaction provide profound insights into the theoretical aspects and offer valuable applications for modeling reaction systems involving the propargyl radicals. METHODS The B3LYP and CCSD(T) methods, combined with the aug-cc-pVnZ (n = T, Q, 5) basis sets, were employed to optimize structures and calculate single-point energies for all species involved in the reaction. The temperature range (200 - 2000 K) and pressure range (0 - 7600 Torr) were used to calculate the bimolecular rate constants for the dominant reaction pathways. The TST, VRC-TST, and RRKM models, with the small curvature tunneling correction, were employed for the kinetic calculations.
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Affiliation(s)
- Hoang T T Trang
- Department of Chemistry, Hanoi Architectural University, Hanoi, Vietnam
| | - Nghiem T Thuong
- School of Chemistry and Life Sciences, Hanoi University of Science and Technology, Hanoi, Vietnam
| | - Tien V Pham
- School of Chemistry and Life Sciences, Hanoi University of Science and Technology, Hanoi, Vietnam.
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Zhang YF, Li W, Wang CY, Huang C, Bian HT, Zhao L. Formation of C 5H 6 isomers: a combination of experimental and computational investigation. Phys Chem Chem Phys 2025; 27:4934-4943. [PMID: 39962987 DOI: 10.1039/d4cp03728f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/28/2025]
Abstract
A propagation mechanism originating from 1,3-cyclopentadienyl, a prearomatic resonantly stabilized radical, makes a significant contribution to the growth of polycyclic aromatic hydrocarbons and soot. 1,3-Cyclopentadiene, as the simplest 5-membered carbon closed-shell molecule that could generate 1,3-cyclopentadienyl via photolysis and H-elimination, is attracting attention from astrochemistry and combustion chemistry communities. The reaction of propargyl (˙C3H3) with ethylene (C2H4) was investigated in a micro SiC reactor under low-pressure (<100 Torr) conditions coupled with tunable synchrotron radiation photoionization and molecular beam mass spectrometry techniques. Their potential energy surfaces were explored by ab initio electronic structure calculations. Subsequently, microscopic kinetics were demonstrated by RRKM/master equation theory in consideration of temperature- and pressure-dependent effects. The analysis of the photoionization efficiency (PIE) analysis at m/z = 66 has confirmed the formation of C5H6 molecules with a cyclic structure, i.e. 1,3-cyclopentadiene, as well as its linear isomer 3-penten-1-yne. Supported by ionization energies and Franck-Condon factors from theoretical predictions, this work proposes the possible formation of C5H6 molecules with two linear isomers 1,2,4-pentatriene and 4-penten-1-yne. Kinetics reveal the discrepancy of product selectivity under diverse temperatures and pressures. Notably, the generation of 1,2,4-pentatriene prevails at high temperatures corresponding to combustion environments, followed closely by 4-penten-1-yne and 3-penten-1-yne formations. Conversely, 1,3-cyclopentadiene shows a strong yield predominance in a vacuum environment within 300-600 K. This finding provides a potential pathway to aromatic hydrocarbon formation, especially in the planetary nebulae and circumstellar envelopes of carbon-rich stars.
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Affiliation(s)
- Yi-Fan Zhang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, 230029, China.
| | - Wang Li
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, 230029, China.
| | - Chang-Yang Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, 230029, China.
| | - Chen Huang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, 230029, China.
| | - Hui-Ting Bian
- Technical Support Center for Prevention and Control of Disastrous Accidents in Metal Smelting, University of Science and Technology Beijing, Beijing, 100083, China.
| | - Long Zhao
- School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui, 230027, China.
- Deep Space Exploration Laboratory, University of Science and Technology of China, Hefei, Anhui, 230026, China
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Hansen N, Gaiser N, Bierkandt T, Oßwald P, Köhler M, Zádor J, Hemberger P. Identification of Dihydropentalenes as Products of the Molecular-Weight Growth Reaction of Cyclopentadienyl Plus Propargyl. J Phys Chem A 2025; 129:1714-1725. [PMID: 39888673 DOI: 10.1021/acs.jpca.4c06549] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2025]
Abstract
The resonance-stabilized cyclopentadienyl (C5H5) and propargyl (C3H3) radicals are important precursors for polycyclic aromatic hydrocarbons (PAHs) and thus play a significant role in molecular-weight growth and soot formation processes under combustion conditions. In this work, we describe an experimental and theoretical investigation of the C5H5 + C3H3 reaction. Experimentally, we studied this reaction in a resistively heated microtubular SiC reactor at a controlled temperature of ∼1150 K and a pressure of 10-20 mbar. The reactants C5H5 and C3H3 were pyrolytically generated from anisole (C6H5OCH3) and propargyl bromide (C3H3Br). We identified the reactants and the C8H8 products isomer-selectively utilizing photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). The experimentally observed predominant formation of dihydropentalenes over the ring-enlargement reaction to styrene is consistent with our theoretical predictions of the kinetics on the newly calculated C8H8 potential energy surface. This work highlights dihydropentalenes as reactants in molecular-weight growth reactions and as potential building blocks in versatile routes for the formation of curved PAHs.
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Affiliation(s)
- Nils Hansen
- Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States
| | - Nina Gaiser
- Institute of Combustion Technology, German Aerospace Center (DLR), 70569 Stuttgart, Germany
| | - Thomas Bierkandt
- Institute of Combustion Technology, German Aerospace Center (DLR), 70569 Stuttgart, Germany
| | - Patrick Oßwald
- Institute of Combustion Technology, German Aerospace Center (DLR), 70569 Stuttgart, Germany
| | - Markus Köhler
- Institute of Combustion Technology, German Aerospace Center (DLR), 70569 Stuttgart, Germany
| | - Judit Zádor
- Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, United States
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute (PSI), 5232 Villigen, Switzerland
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Xu G, Wang H, Zhang J, Gao J, Guan J, Xu Q, Truhlar DG, Wang Z. Combining synchrotron vacuum-ultraviolet photoionization mass spectrometry and gas chromatography-mass spectrometry for isomer-specific mechanistic analysis with application to the benzyl self-reaction. Nat Commun 2024; 15:10755. [PMID: 39737901 DOI: 10.1038/s41467-024-53889-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2024] [Accepted: 10/25/2024] [Indexed: 01/01/2025] Open
Abstract
Elucidating the formation mechanism of polycyclic aromatic hydrocarbons (PAHs) is crucial to understand processes in the contexts of combustion, environmental science, astrochemistry, and nanomaterials synthesis. An excited electronic-state pathway has been proposed to account for the formation of 14π aromatic anthracene in the benzyl (b-C7H7) self-reaction. Here, to improve our understanding of anthracene formation, we investigate C7H7 bimolecular reactions in a tubular SiC microreactor through an isomer-resolved method that combines in situ synchrotron-radiation VUV photoionization mass spectrometry and ex-situ gas chromatography-mass spectrometry. We observe the formation of o-tolyl (o-C7H7) radical isomer, and identify several C14H10 products (diphenylacetylene, phenanthrene and anthracene) and key C14H14 and C14H12 intermediates. These isomer-specific results support the occurrence of reactions on the electronic ground-state potential energy surface, with no evidence for key intermediates of the proposed excited-state pathway as the key pathway. Furthermore, theoretical calculations unveil new facile reaction pathways that may contribute to the enhanced production of anthracene, and these mechanistic findings are further substantiated by pyrolysis experiments. The results add insight into the molecular formation of PAHs in C7H7 bimolecular reaction, and contribute to establishing accurate models to predict PAH chemistry in diverse laboratory, environmental, and extraterrestrial contexts.
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Affiliation(s)
- Guangxian Xu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China
| | - Hong Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China
| | - Jinyang Zhang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China
| | - Jiao Gao
- School of Pharmacy, Anhui Medical College, Hefei, Anhui, PR China
| | - Jiwen Guan
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China.
| | - Qiang Xu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China
| | - Donald G Truhlar
- Department of Chemistry, University of Minnesota, Minneapolis, MN, USA.
| | - Zhandong Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, PR China.
- State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui, PR China.
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Kelly PD, Turner JA, Shiels OJ, da Silva G, Blanksby SJ, Poad BLJ, Trevitt AJ. Don't forget the trans: double bond isomerism radical-acetylene growth reactions affect the primary stages of PAH and soot formation. Phys Chem Chem Phys 2024; 27:83-95. [PMID: 39652099 DOI: 10.1039/d4cp03554b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2024]
Abstract
In combustion, acetylene is a key species in molecular-weight growth reactions that form polycyclic aromatic hydrocarbons (PAHs) and ultimately soot particles. Radical addition to acetylene generates a vinyl radical intermediate, which has both trans and cis isomers. This isomerism can lead to profound changes in product distributions that are as yet insufficiently investigated. Herein, we explore acetylene addition to substituted trans-vinyl radicals, including potential rearrangement to cis structures, for eight combustion-related hydrocarbon radicals calculated using a composite method (G3X-K). Of these eight systems, the phenyl trans- and cis-Bittner-Howard HACA (hydrogen abstraction, C2H2 Addition) process, where acetylene successively adds to a phenyl radical via a β-styryl intermediate, is simulated using a unified Master Equation model. Including the trans-Bittner-Howard pathway changes the products significantly at all simulated temperatures (550-1800 K) and pressures (5.33 × 102-107 Pa), relative to a cis-only model. Typically, naphthalene remains the dominant product, but its abundance decreases at higher temperatures and pressures. For example, at 1200 K and 105 Pa, its branching ratio decreases from 78.5% to 62.9% when the trans pathway is included. At higher temperatures this decrease corresponds to the formation of alternative C10H8 isomers, including the cis product benzofulvene with 8% maximum abundance at 1200 K and 5.33 × 102 Pa, and E-2-ethynyl-1-phenylethylene, a trans product with 26% maximum abundance at 1800 K, with little pressure dependence. At higher pressures, our model predicts a range of C10H9 radicals, including resonance-stabilised radicals (RSRs). The impact of trans-vinyl radical chemistry in reactive environments means that they are essential to accurately describe combustion reactions and inhibit soot formation.
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Affiliation(s)
- Patricia D Kelly
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
| | - Jack A Turner
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
| | - Oisin J Shiels
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
| | - Gabriel da Silva
- Department of Chemical Engineering, The University of Melbourne, Melbourne, Victoria, Australia
| | - Stephen J Blanksby
- Central Analytical Research Facility and the School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, Australia
| | - Berwyck L J Poad
- Central Analytical Research Facility and the School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland, Australia
| | - Adam J Trevitt
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
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9
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Pham TV, Nguyen NT, Huong TT. A kinetic and mechanistic study of the self-reaction between two propargyl radicals. J Mol Model 2024; 30:394. [PMID: 39499352 DOI: 10.1007/s00894-024-06191-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2024] [Accepted: 10/23/2024] [Indexed: 11/07/2024]
Abstract
CONTEXT The propargyl radical plays a critical role in various chemical processes, including hydrocarbon combustion, flame synthesis, and interstellar chemistry. Its unique stability arises from the delocalization of π-electrons, allowing it to participate in a wide range of reactions despite being a radical. The self-reaction of propargyl radicals is a fundamental step in synthesizing polycyclic aromatic hydrocarbons. In this work, therefore, a computational study into the C3H3 + C3H3 potential energy surface has been carefully characterized. The calculated results indicate that the reaction can occur by H-abstraction or addition of two propargyl radicals together. The H-abstraction mechanism can create the products P3 (H2CCC + H3CCCH) and P4 (H2CCCH2 + HCCCH) but the energy barriers of the two H-abstraction channels are very high (from 12 to 22 kcal/mol). In contrast, the addition mechanism of two propargyl radicals forming the intermediates (I1, I5, I12) and the bimolecular products (P1, P2, P7, P11, P12) are dominant. Among the bimolecular products, the P11 (C6H4 + H2) product is the most energetically favorable, and the channel leading to this product is also the most preferred path compared to all other paths throughout the PES. The calculated enthalpy changes of various reaction paths in this study are in good agreement with the available literature data, indicating that the CCSD(T) method is suitable for the title reaction. The overall rate constant of the reaction depends on both temperature and pressure, reducing with temperature but rising with pressure. The calculated results agree closely with the available experimental values and previous calculated data. Thus, it can be affirmed that in addition to the CASPT2 method as applied in the study of Georgievskii et al. (Phys. Chem. Chem. Phys., 2007, 9, 4259-4268), the CCSD(T) method is also very good for the self-reaction of two propargyl radicals. METHODS The M06-2X and CCSD(T) methods with the aug-cc-pVTZ basis set were used to optimize and calculate single-point energies for all species of the reaction. The bimolecular rate constants of the dominant reaction paths were predicted in the temperature and pressure ranges of 300-1800 K and 0 - 76,000 Torr, respectively, using the VTST and RRKM models with Eckart tunneling correction for the H-shift steps.
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Affiliation(s)
- Tien V Pham
- School of Chemistry and Life Sciences, Hanoi University of Science and Technology, Hanoi, Vietnam.
| | - Nghia T Nguyen
- School of Chemistry and Life Sciences, Hanoi University of Science and Technology, Hanoi, Vietnam
| | - Tran Thu Huong
- School of Chemistry and Life Sciences, Hanoi University of Science and Technology, Hanoi, Vietnam
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10
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Byrne AN, Xue C, Van Voorhis T, McGuire BA. Sensitivity analysis of aromatic chemistry to gas-phase kinetics in a dark molecular cloud model. Phys Chem Chem Phys 2024; 26:26734-26747. [PMID: 39431338 DOI: 10.1039/d4cp03229b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2024]
Abstract
The increasingly large number of complex organic molecules detected in the interstellar medium necessitates robust kinetic models that can be relied upon for investigating the involved chemical processes. Such models require rate coefficients for each of the thousands of reactions; the values of these are often estimated or extrapolated, leading to large uncertainties that are rarely quantified. We have performed a global Monte Carlo and a more local one-at-a-time sensitivity analysis on the gas-phase rate coefficients in a 3-phase dark cloud model. Time-dependent sensitivities have been calculated using four metrics to determine key reactions for the overall network as well as for the cyanonaphthalene molecule in particular, an important interstellar species that is severely under-produced by current models. All four metrics find that reactions involving small, reactive species that initiate hydrocarbon growth have large effects on the overall network. Cyanonaphthalene is most sensitive to a number of these reactions as well as ring-formation of the phenyl cation (C6H5+) and aromatic growth from benzene to naphthalene. Future efforts should prioritize constraining rate coefficients of key reactions and expanding the network surrounding these processes. These results highlight the strength of sensitivity analysis techniques to identify critical processes in complex chemical networks, such as those often used in astrochemical modeling.
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Affiliation(s)
- Alex N Byrne
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Ci Xue
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Troy Van Voorhis
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
| | - Brett A McGuire
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
- National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
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11
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Couch DE, San Marchi MM, Hansen N. Experimental observation of molecular-weight growth by the reactions of o-benzyne with benzyl radicals. Phys Chem Chem Phys 2024; 26:24833-24840. [PMID: 39290192 DOI: 10.1039/d4cp02560a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/19/2024]
Abstract
The chemistry of ortho-benzyne (o-C6H4) is of fundamental importance due to its role as an essential molecular building block in molecular-weight growth reactions. Here, we report on an experimental investigation of the reaction of o-C6H4 with benzyl (C7H7) radicals in a well-controlled flash pyrolysis experiment using a resistively heated SiC microtubular reactor at temperatures of 800-1600 K and pressures near 30 torr. To this end, the reactants o-C6H4 and C7H7 were pyrolytically generated from 1,2-diiodobenzene and benzyl bromide, respectively. Using molecular-beam time-of-flight mass spectrometry, we found that o-C6H4 associates with the benzyl to form C13H11 radicals, which decompose at higher temperatures via H-loss to form closed-shell C13H10 molecules. Our experimental results agree with earlier theoretical calculations by Matsugi and Miyoshi [Phys. Chem. Chem. Phys., 2012, 14, 9722-9728], who predicted the formation of fluorene (C13H10) + H to be the dominant reaction channel. At temperatures above 1400 K, we also observed the formation of C13H9 radicals, most likely the resonance-stabilized fluorenyl π-radical. Our study confirms that molecular-mass growth via the o-C6H4 + C7H7 reaction provides a versatile pathway for introducing five-membered rings, and hence curved structures, into polycyclic aromatic hydrocarbons.
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Affiliation(s)
- David E Couch
- Department of Chemistry, United States Air Force Academy, CO 80840, USA
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA.
| | - Myrsini M San Marchi
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA.
| | - Nils Hansen
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA.
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12
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Flores J, Ruscitti M, Khani S, Reilly NJ. Electronic Spectrum of α-Hydrofulvenyl Radical (C 6H 7), and a Simple and Accurate Recipe for Predicting Adiabatic Ionization Energies of Resonance-Stabilized Hydrocarbon Radicals. J Phys Chem A 2024; 128:8123-8136. [PMID: 39264134 DOI: 10.1021/acs.jpca.4c04746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/13/2024]
Abstract
Using a combination of resonant two-photon two-color ionization (R2C2PI) and laser-induced fluorescence/dispersed fluorescence spectroscopy, we have examined the A ~ 2A″ ← X ~ 2A″ transition of the resonance-stabilized α-hydrofulvenyl radical, produced from methylcyclopentadiene dimer in a jet-cooled discharge. Like the related 1,4-pentadienyl and cyclohexadienyl radicals, the α-hydrofulvenyl Ã-state lifetime is orders of magnitude shorter than the predicted f-value implies, indicative of rapid nonradiative decay. The transition is fully allowed by symmetry but considerably weakened by transition moment interference. Intensity borrowing among a' modes brings about static (i.e., Condon) and vibronic (i.e., Herzberg-Teller) moments of similar size, the result being a spectrum substantially less origin-dominated than is usually observed for extensively delocalized radicals. Twenty A ~ -state modes and twelve X ~ -state modes are identified with high confidence and assignments for several others are suggested. In addition, from a series of two-color appearance potential scans with the A ~ -state zero-point level serving as an intermediate, we obtain a field-free adiabatic ionization energy (AIE) of 7.012(1) eV. For a set of 21 resonance-stabilized radicals bearing 5 to 11 carbon atoms, it emerges that the field-free AIE obtained by R2C2PI methods under jet-cooled conditions lies very close to the average of B3LYP/6-311G++(d,p) (with harmonic zero-point energy) and CBS-QB3 0 K calculations, with a mean absolute deviation of only 0.010(7) eV (approximately 1 kJ/mol). On average, this represents a nearly 10-fold improvement in accuracy over CBS-QB3 predictions for the same set of radicals.
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Affiliation(s)
- Jonathan Flores
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
| | - Massimo Ruscitti
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
| | - Sima Khani
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
| | - Neil J Reilly
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
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13
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Castiñeira Reis M, Martínez Núñez E, Fernández Ramos A. Comprehensive computational automated search of barrierless reactions leading to the formation of benzene and other C 6-membered rings. SCIENCE ADVANCES 2024; 10:eadq4077. [PMID: 39259783 PMCID: PMC11389753 DOI: 10.1126/sciadv.adq4077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Accepted: 08/06/2024] [Indexed: 09/13/2024]
Abstract
We present the systematic exploration of various potential energy surfaces for systems with C6H6-x (x = 0, 1, 2, or 3) empirical formula using an automatic search approach. The primary objective of this study is to identify reaction pathways that lead to the creation of benzene, o-benzyne, and other rings. These pathways initiate with a barrierless recombination reaction and involve subsequent isomerization reactions with submerged transition states until the final product is reached. The reported reaction profiles are consistent with the existing conditions in the interstellar medium if the hot complex formed can cool down through radiative relaxation. Recent studies on the deactivation of polyaromatic hydrocarbons (PAHs) support the possibility of these reactions taking place. The C6-membered rings are considered precursors of PAHs, and our focus is on identifying pathways originating from the barrierless recombination of reactive molecules known to exist in the interstellar medium, with potential implications in other environments.
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Affiliation(s)
- Marta Castiñeira Reis
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Campus Vida, 15782, Universidade de Santiago de Compostela, C/Jenaro de la Fuente s/n, Santiago de Compostela, Spain
| | - Emilio Martínez Núñez
- Departamento de Química Física, Facultade de Química, Campus Vida, 15782, Universidade de Santiago de Compostela, Avda. das Ciencias s/n, Santiago de Compostela, Spain
| | - Antonio Fernández Ramos
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS), Campus Vida, 15782, Universidade de Santiago de Compostela, C/Jenaro de la Fuente s/n, Santiago de Compostela, Spain
- Departamento de Química Física, Facultade de Química, Campus Vida, 15782, Universidade de Santiago de Compostela, Avda. das Ciencias s/n, Santiago de Compostela, Spain
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14
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Xu Q, Zhang J, Liu B, Wang H, Xu G, Gao J, Wang Z, Guan J. Probing the Reaction of Propargyl Radical with Molecular Oxygen by Synchrotron VUV Photoionization Mass Spectrometry. J Phys Chem A 2024; 128:7105-7113. [PMID: 39151122 DOI: 10.1021/acs.jpca.4c03294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2024]
Abstract
Self-reaction of propargyl (C3H3) radical is the main pathway to benzene, the formation of which is the rate-controlling step toward the formation of polycyclic aromatic hydrocarbons (PAHs) and soot. Oxidation of C3H3 is a promising strategy to inhibit the formation of hazardous PAHs and soot. In the present study, we studied the C3H3 + O2 reaction from 650 to 1100 K in a laminar flow reactor and identified the intermediates and products by synchrotron VUV photoionization mass spectrometry. 2-Propynal, ethenone, formaldehyde, CO, CO2, C2H2, C2H4, and C3O2 were identified. Among them, 2-propynal, ethenone, and formaldehyde provided direct evidence for the branching reaction of C3H3 + O2 → HCCCHO + OH, C3H3 + O2 → H2CCO + CHO, and C3H3 + O2 → H2CO + CHCO, respectively. Potential energy surface calculation and mechanistic analysis of the C3O2 formations implied that C3H3 + O2 → CCCHO + H2O and C3H3 + O2 → HCCCO + H2O could occur, despite lacking direct observations of CCCHO and HCCCO radicals. The formation of ethenone and CO suggested the occurrence of the two CO elimination channels. We incorporated these validated reactions and the corresponding rate coefficients in the kinetic model of NUIGMech1.3, and the simulation showed obvious improvements toward the measured mole fractions of C3H3 and H2CCO, suggesting that the new C3H3 + O2 reaction channels were crucial in the overall combustion modeling of the important intermediate propyne (C3H4).
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Affiliation(s)
- Qiang Xu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
| | - Jinyang Zhang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
| | - Bingzhi Liu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
| | - Hong Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
| | - Guangxian Xu
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
| | - Jiao Gao
- School of Pharmacy, Anhui Medical College, Hefei 230601, Anhui, P. R. China
| | - Zhandong Wang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
- State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China
| | - Jiwen Guan
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, Anhui, P. R. China
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15
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Hrodmarsson HR, Garcia GA, Bourehil L, Nahon L, Gans B, Boyé-Péronne S, Guillemin JC, Loison JC. The isomer distribution of C 6H 6 products from the propargyl radical gas-phase recombination investigated by threshold-photoelectron spectroscopy. Commun Chem 2024; 7:156. [PMID: 38997498 PMCID: PMC11245511 DOI: 10.1038/s42004-024-01239-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Accepted: 07/02/2024] [Indexed: 07/14/2024] Open
Abstract
The resonance-stabilization of the propargyl radical (C3H3) makes it among the most important reactive intermediates in extreme environments and grants it a long enough lifetime to recombine in both terrestrial combustion media and cold molecular clouds in space. This makes the propargyl self-reaction a pivotal step in the formation of benzene, the first aromatic ring, to eventually lead to polycyclic aromatic hydrocarbons in a variety of environments. In this work, by producing propargyl radicals in a flow tube where propyne reacted with F atoms and probing the reaction products by mass-selected threshold-photoelectron spectroscopy (TPES), we identified eight C6H6 products in total, including benzene. On top of providing the first comprehensive measurements of the branching ratios of the eight identified C6H6 isomers in the propargyl self reaction products (4 mbar, 298 K conditions), this study also highlights the advantages and disadvantages of using isomer-selective TPES to identify and quantify reaction products.
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Affiliation(s)
- Helgi Rafn Hrodmarsson
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, F-91192, Gif sur Yvette, France.
- Univ Paris Est Créteil and Université Paris Cité, CNRS, LISA UMR 7583, 94010, Créteil, France.
| | - Gustavo A Garcia
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, F-91192, Gif sur Yvette, France
| | - Lyna Bourehil
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, F-91192, Gif sur Yvette, France
| | - Laurent Nahon
- Synchrotron SOLEIL, L'Orme des Merisiers, St. Aubin, F-91192, Gif sur Yvette, France
| | - Bérenger Gans
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, F-91405, Orsay, France
| | - Séverine Boyé-Péronne
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, F-91405, Orsay, France
| | - Jean-Claude Guillemin
- Univ Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR - UMR6226, F-35000, Rennes, France
| | - Jean-Christophe Loison
- Institut des Sciences Moléculaires, CNRS, Université de Bordeaux, F-33400, Talence, France.
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16
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Changala PB, Franke PR, Stanton JF, Ellison GB, McCarthy MC. Direct Probes of π-Delocalization in Prototypical Resonance-Stabilized Radicals: Hyperfine-Resolved Microwave Spectroscopy of Isotopic Propargyl and Cyanomethyl. J Am Chem Soc 2024; 146:1512-1521. [PMID: 38170910 DOI: 10.1021/jacs.3c11220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Delocalization of the unpaired electron in π-conjugated radicals has profound implications for their chemistry, but direct and quantitative characterization of this electronic structure in isolated molecules remains challenging. We apply hyperfine-resolved microwave rotational spectroscopy to rigorously probe π-delocalization in propargyl, CH2CCH, a prototypical resonance-stabilized radical and key reactive intermediate. Using the spectroscopic constants derived from the high-resolution cavity Fourier transform microwave measurements of an exhaustive set of 13C- and 2H-substituted isotopologues, together with high-level ab initio calculations of zero-point vibrational effects, we derive its precise semiexperimental equilibrium geometry and quantitatively characterize the spatial distribution of its unpaired electron. Our results highlight the importance of considering both spin-polarization and orbital-following contributions when interpreting the isotropic hyperfine coupling constants of π radicals. These physical insights are strengthened by a parallel analysis of the isoelectronic species cyanomethyl, CH2CN, using new 13C measurements also reported in this work. A detailed comparison of the structure and electronic properties of propargyl, cyanomethyl, and other closely related species allows us to correlate trends in their chemical bonding and electronic structure with critical changes in their reactivity and thermochemistry.
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Affiliation(s)
- P Bryan Changala
- Center for Astrophysics|Harvard & Smithsonian, Cambridge, Massachusetts 02138, United States
| | - Peter R Franke
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - John F Stanton
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - G Barney Ellison
- Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
| | - Michael C McCarthy
- Center for Astrophysics|Harvard & Smithsonian, Cambridge, Massachusetts 02138, United States
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17
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Li W, Yang J, Zhao L, Couch D, Marchi MS, Hansen N, Morozov AN, Mebel AM, Kaiser RI. Gas-phase preparation of azulene (C 10H 8) and naphthalene (C 10H 8) via the reaction of the resonantly stabilized fulvenallenyl and propargyl radicals. Chem Sci 2023; 14:9795-9805. [PMID: 37736626 PMCID: PMC10510771 DOI: 10.1039/d3sc03231k] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Accepted: 08/23/2023] [Indexed: 09/23/2023] Open
Abstract
Synthetic routes to the 10π Hückel aromatic azulene (C10H8) molecule, the simplest polycyclic aromatic hydrocarbon carrying an adjacent five- and seven-membered ring, have been of fundamental importance due to the role of azulene - a structural isomer of naphthalene - as an essential molecular building block of saddle-shaped carbonaceous nanostructures such as curved nanographenes and nanoribbons. Here, we report on the very first gas phase preparation of azulene by probing the gas-phase reaction between two resonantly stabilized radicals, fulvenallenyl and propargyl , in a molecular beam through isomer-resolved vacuum ultraviolet photoionization mass spectrometry. Augmented by electronic structure calculations, the novel Fulvenallenyl Addition Cyclization Aromatization (FACA) reaction mechanism affords a versatile concept for introducing the azulene moiety into polycyclic aromatic systems thus facilitating an understanding of barrierless molecular mass growth processes of saddle-shaped aromatics and eventually carbonaceous nanoparticles (soot, interstellar grains) in our universe.
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Affiliation(s)
- Wang Li
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Jiuzhong Yang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
| | - Long Zhao
- National Synchrotron Radiation Laboratory, University of Science and Technology of China Hefei Anhui 230029 China
- School of Nuclear Science and Technology, University of Science and Technology of China Hefei Anhui 230027 China
| | - David Couch
- Combustion Research Facility, Sandia National Laboratories Livermore CA 94551 USA
| | - Myrsini San Marchi
- Combustion Research Facility, Sandia National Laboratories Livermore CA 94551 USA
| | - Nils Hansen
- Combustion Research Facility, Sandia National Laboratories Livermore CA 94551 USA
| | - Alexander N Morozov
- Department of Chemistry and Biochemistry, Florida International University Miami FL 33199 USA
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University Miami FL 33199 USA
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawaii at Manoa Honolulu HI 96822 USA
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18
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Yang Z, Galimova GR, He C, Goettl SJ, Paul D, Lu W, Ahmed M, Mebel AM, Li X, Kaiser RI. Gas-phase formation of the resonantly stabilized 1-indenyl (C 9H 7•) radical in the interstellar medium. SCIENCE ADVANCES 2023; 9:eadi5060. [PMID: 37682989 PMCID: PMC10491290 DOI: 10.1126/sciadv.adi5060] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 08/07/2023] [Indexed: 09/10/2023]
Abstract
The 1-indenyl (C9H7•) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C(3P)] with styrene (C6H5C2H3) and propargyl (C3H3•) with phenyl (C6H5•). Macroscopic environments like molecular clouds act as natural low-temperature laboratories, where rapid molecular mass growth to 1-indenyl and subsequently complex PAHs involving vinyl side-chained aromatics and aryl radicals can occur. These reactions may account for the formation of PAHs and their derivatives in the interstellar medium and carbonaceous chondrites and could close the gap of timescales of their production and destruction in our carbonaceous universe.
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Affiliation(s)
- Zhenghai Yang
- Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA
| | - Galiya R. Galimova
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
| | - Chao He
- Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA
| | - Shane J. Goettl
- Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA
| | - Dababrata Paul
- Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Alexander M. Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA
| | - Xiaohu Li
- Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, P. R. China
- Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, P. R. China
| | - Ralf I. Kaiser
- Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA
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19
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McGee CJ, McGinnis KR, Jarrold CC. Trend in the Electron Affinities of Fluorophenyl Radicals ·C 6H 5-xF x (1 ≤ x ≤ 4). J Phys Chem A 2023; 127:7264-7273. [PMID: 37603043 DOI: 10.1021/acs.jpca.3c04327] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/22/2023]
Abstract
The electron affinities (EAs) of a series of ·C6H5-xFx (1 ≤ x ≤ 4) fluorophenyl radicals are determined from the photoelectron spectra of their associated fluorophenide anions generated from C6H6-xFx (1 ≤ x ≤ 4) fluorobenzene precursors. The spectra show a near-linear incremental increase in EA of 0.4 eV/x. The spectra exhibit vibrationally unresolved and broad detachment transitions consistent with significant differences in the molecular structures of the anion and neutral radical species. The experimental EAs and broad spectra are consistent with density functional theory calculations on these species. While the anion detachment transitions all involve an electron in a non-bonding orbital, the differences in structure between the neutral and anion are in part due to repulsion between the lone pair on the C-center on which the excess charge is localized and neighboring F atoms. The C6H5-xFx- (2 ≤ x ≤ 4) spectra show features at lower binding energy that appear to be due to constitutional isomers formed in the ion source.
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Affiliation(s)
- Conor J McGee
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Kristen Rose McGinnis
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Caroline Chick Jarrold
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
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20
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He C, Kaiser RI, Lu W, Ahmed M, Krasnoukhov VS, Pivovarov PS, Zagidullin MV, Azyazov VN, Morozov AN, Mebel AM. Unconventional gas-phase preparation of the prototype polycyclic aromatic hydrocarbon naphthalene (C 10H 8) via the reaction of benzyl (C 7H 7) and propargyl (C 3H 3) radicals coupled with hydrogen-atom assisted isomerization. Chem Sci 2023; 14:5369-5378. [PMID: 37234886 PMCID: PMC10208037 DOI: 10.1039/d3sc00911d] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 04/19/2023] [Indexed: 05/28/2023] Open
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium and in meteorites such as Murchison and Allende and signify the missing link between resonantly stabilized free radicals and carbonaceous nanoparticles (soot particles, interstellar grains). However, the predicted lifetime of interstellar PAHs of some 108 years imply that PAHs should not exist in extraterrestrial environments suggesting that key mechanisms of their formation are elusive. Exploiting a microchemical reactor and coupling these data with computational fluid dynamics (CFD) simulations and kinetic modeling, we reveal through an isomer selective product detection that the reaction of the resonantly stabilized benzyl and the propargyl radicals synthesizes the simplest representative of PAHs - the 10π Hückel aromatic naphthalene (C10H8) molecule - via the novel Propargyl Addition-BenzAnnulation (PABA) mechanism. The gas-phase preparation of naphthalene affords a versatile concept of the reaction of combustion and astronomically abundant propargyl radicals with aromatic radicals carrying the radical center at the methylene moiety as a previously passed over source of aromatics in high temperature environments thus bringing us closer to an understanding of the aromatic universe we live in.
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Affiliation(s)
- Chao He
- Department of Chemistry, University of Hawai'i at Mānoa Honolulu HI 96822 USA
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Mānoa Honolulu HI 96822 USA
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| | - Vladislav S Krasnoukhov
- Lebedev Physical Institute Samara 443011 Russian Federation
- Samara National Research University Samara 443086 Russian Federation
| | - Pavel S Pivovarov
- Samara National Research University Samara 443086 Russian Federation
| | | | | | - Alexander N Morozov
- Department of Chemistry and Biochemistry, Florida International University Miami Florida 33199 USA
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University Miami Florida 33199 USA
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21
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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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22
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He C, Kaiser RI, Lu W, Ahmed M, Reyes Y, Wnuk SF, Mebel AM. Exotic Reaction Dynamics in the Gas-Phase Preparation of Anthracene (C 14H 10) via Spiroaromatic Radical Transients in the Indenyl-Cyclopentadienyl Radical-Radical Reaction. J Am Chem Soc 2023; 145:3084-3091. [PMID: 36701838 DOI: 10.1021/jacs.2c12045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The gas-phase reaction between the 1-indenyl (C9H7•) radical and the cyclopentadienyl (C5H5•) radical has been investigated for the first time using synchrotron-based mass spectrometry coupled with a pyrolytic reactor. Soft photoionization with tunable vacuum ultraviolet photons afforded for the isomer-selective identification of the production of phenanthrene, anthracene, and benzofulvalene (C14H10). The classical theory prevalent in the literature proposing that radicals combine only at their specific radical centers is challenged by our discovery of an unusual reaction pathway that involves a barrierless combination of a resonantly stabilized hydrocarbon radical with an aromatic radical at the carbon atom adjacent to the traditional C1 radical center; this unconventional addition is followed by substantial isomerization into phenanthrene and anthracene via a category of exotic spiroaromatic intermediates. This result leads to a deeper understanding of the evolution of the cosmic carbon budget and provides new methodologies for the bottom-up synthesis of unique spiroaromatics that may be relevant for the synthesis of more complex aromatic carbon skeletons in deep space.
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Affiliation(s)
- Chao He
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Manoa, Honolulu, Hawaii 96822, United States
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Yahaira Reyes
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Stanislaw F Wnuk
- 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
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23
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Galimova GR, Mebel AM, Goettl SJ, Yang Z, Kaiser RI. A crossed molecular beams and computational study on the unusual reactivity of banana bonds of cyclopropane (c-C 3H 6; ) through insertion by ground state carbon atoms (C( 3P j)). Phys Chem Chem Phys 2022; 24:22453-22463. [PMID: 36102937 DOI: 10.1039/d2cp03293g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The mechanism and chemical dynamics of the reaction of ground electronic state atomic carbon C(3Pj) with cyclopropane c-C3H6 have been explored by combining crossed molecular beams experiments with electronic structure calculations of the pertinent triplet C4H6 potential energy surface and statistical computations of product branching ratios under single-collision conditions. The experimental findings suggest that the reaction proceeds via indirect scattering dynamics through triplet C4H6 reaction intermediate(s) leading to C4H5 product(s) plus atomic hydrogen via a tight exit transition state, with the overall reaction exoergicity evaluated as 231 ± 52 kJ mol-1. The calculations indicate that C(3Pj) can easily insert into one of the three equivalent C-C 'banana' bonds of cyclopropane overcoming a low barrier of only 2 kJ mol-1 following the formation of a van der Waals reactant complex stabilized by 15 kJ mol-1. The carbon atom insertion into one of the six C-H bonds is also feasible via a slightly higher barrier of 5 kJ mol-1. These results highlight an unusual reactivity of cyclopropane's banana C-C bonds, which behave more like unsaturated C-C bonds with a π-character than saturated σ C-C bonds, which are known to be generally unreactive toward the ground electronic state atomic carbon such as in ethane (C2H6). The statistical theory predicts the overall product branching ratios at the experimental collision energy as 50% for 1-butyn-4-yl, 33% for 1,3-butadien-2-yl, i-C4H5, and 11% for 1,3-butadien-1-yl, n-C4H5, with i-C4H5 (230 kJ mol-1 below the reactants) favored by the C-C insertion providing the best match with the experimentally observed reaction exoergicity. The C(3Pj) + c-C3H6 reaction is predicted to be a source of C4H5 radicals under the conditions where its low entrance barriers can be overcome, such as in planetary atmospheres or in circumstellar envelopes but not in cold molecular clouds. Both i- and n-C4H5 can further react with acetylene eventually producing the first aromatic ring and hence, the reaction of the atomic carbon with c-C3H6 can be considered as an initial step toward the formation of benzene.
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Affiliation(s)
- Galiya R Galimova
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA.
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA.
| | - Shane J Goettl
- Department of Chemistry, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA.
| | - Zhenghai Yang
- Department of Chemistry, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA.
| | - Ralf I Kaiser
- Department of Chemistry, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA.
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24
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Gao H, Tang H. Temperature Effect on Formation of Polycyclic Aromatic Hydrocarbons in Acetylene Pyrolysis. ChemistrySelect 2022. [DOI: 10.1002/slct.202201893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- He Gao
- College of Energy and Power Engineering Nanjing University of Aeronautics and Astronautics 29-Yudao St. Nanjing 210016, Jiangsu Province China
| | - Hao Tang
- College of Energy and Power Engineering Nanjing University of Aeronautics and Astronautics 29-Yudao St. Nanjing 210016, Jiangsu Province China
- Aero-engine Thermal Environment and Structure Key Laboratory of Ministry of Industry and Information Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016, Jiangsu Province China
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25
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Field-Theodore TE, Taylor PR. Interstellar hide and go seek: C 3H 4O. There and back (again). Phys Chem Chem Phys 2022; 24:19184-19198. [PMID: 35730752 DOI: 10.1039/d2cp00995a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The molecular species C3H4O represents a striking example of an astrochemical conundrum. With more than 60 structural isomers theoretically possible, to date only acrolein (CH2CHCHO) has been identified in the Sgr B2(N) region of the interstellar medium (ISM). The topography of the singlet potential energy surface is complicated, with three low-lying minima predicted to be almost isoenergetic: cis and trans-acrolein, and methylketene (CH3CHCO). Our CCSD(T)/cc-pVTZ calculations confirm that methylketene is energetically lower than cis-acrolein, lying only 1.9 kJ mol-1 above the trans-isomer, which is the global minimum. In this respect, methylketene is a promising candidate for interstellar observation. Unfortunately, however, despite several searches its astronomical detection has been unsuccessful. To this end, the key question is whether in fact methylketene exists as a discrete chemical entity in the ISM at all? In this paper, we present a detailed examination of the C3H4O potential energy surface, with specific focus on formation pathways. CCSD(T)/cc-pVTZ calculations enable a more elaborate interpretation of reaction mechanisms than was published hitherto. Our results show that gauche-propargyl alcohol and syn and anti-allenol emerge as interesting new targets for observational astronomers in TMC-1: given the recent discovery of the propargyl radical in this region, barrierless product channels involving OH˙ lend support to their candidacy as possible interstellar species. Finally, this work provides accurate spectral data of these three potential molecules, to be used for searches in interstellar space.
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Affiliation(s)
| | - Peter R Taylor
- School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China.
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26
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Reizer E, Viskolcz B, Fiser B. Formation and growth mechanisms of polycyclic aromatic hydrocarbons: A mini-review. CHEMOSPHERE 2022; 291:132793. [PMID: 34762891 DOI: 10.1016/j.chemosphere.2021.132793] [Citation(s) in RCA: 62] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Revised: 09/18/2021] [Accepted: 11/02/2021] [Indexed: 06/13/2023]
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are mostly formed during the incomplete combustion of organic materials, but their importance and presence in materials science, and astrochemistry has also been proven. These carcinogenic persistent organic pollutants are essential in the formation of combustion generated particles as well. Due to their significant impact on the environment and human health, to understand the formation and growth of PAHs is essential. Therefore, the most important growth mechanisms are reviewed, and presented here from the past four decades (1981-2021) to initiate discussions from a new perspective. Although, the collected and analyzed observations are derived from both experimental, and computational studies, it is neither a systematic nor a comprehensive review. Nevertheless, the mechanisms were divided into three main categories, acetylene additions (e.g. HACA), vinylacetylene additions (HAVA), and radical reactions, and discussed accordingly.
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Affiliation(s)
- Edina Reizer
- Institute of Chemistry, University of Miskolc, H-3515, Miskolc, Miskolc-Egyetemváros, Hungary; Higher Education and Industrial Cooperation Centre, University of Miskolc, H-3515, Miskolc-Egyetemváros, Hungary
| | - Béla Viskolcz
- Institute of Chemistry, University of Miskolc, H-3515, Miskolc, Miskolc-Egyetemváros, Hungary; Higher Education and Industrial Cooperation Centre, University of Miskolc, H-3515, Miskolc-Egyetemváros, Hungary
| | - Béla Fiser
- Institute of Chemistry, University of Miskolc, H-3515, Miskolc, Miskolc-Egyetemváros, Hungary; Higher Education and Industrial Cooperation Centre, University of Miskolc, H-3515, Miskolc-Egyetemváros, Hungary; Ferenc Rákóczi II. Transcarpathian Hungarian College of Higher Education, UA, 90200, Beregszász, Transcarpathia, Ukraine.
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27
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Kaiser RI, Zhao L, Lu W, Ahmed M, Krasnoukhov VS, Azyazov VN, Mebel AM. Unconventional excited-state dynamics in the concerted benzyl (C 7H 7) radical self-reaction to anthracene (C 14H 10). Nat Commun 2022; 13:786. [PMID: 35145103 PMCID: PMC8831467 DOI: 10.1038/s41467-022-28466-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Accepted: 01/25/2022] [Indexed: 12/20/2022] Open
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are prevalent in deep space and on Earth as products in combustion processes bearing direct relevance to energy efficiency and environmental remediation. Reactions between hydrocarbon radicals in particular have been invoked as critical molecular mass growth processes toward cyclization leading to these PAHs. However, the mechanism of the formation of PAHs through radical – radical reactions are largely elusive. Here, we report on a combined computational and experimental study of the benzyl (C7H7) radical self-reaction to phenanthrene and anthracene (C14H10) through unconventional, isomer-selective excited state dynamics. Whereas phenanthrene formation is initiated via a barrierless recombination of two benzyl radicals on the singlet ground state surface, formation of anthracene commences through an exotic transition state on the excited state triplet surface through cycloaddition. Our findings challenge conventional wisdom that PAH formation via radical-radical reactions solely operates on electronic ground state surfaces and open up a previously overlooked avenue for a more “rapid” synthesis of aromatic, multi-ringed structures via excited state dynamics in the gas phase. The reaction of benzyl radical self-reaction to anthracene opens-up a previously overlooked avenue for a more efficient synthesis of aromatic, multi-ringed structures via excited state dynamics in the gas phase.
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Affiliation(s)
- Ralf I Kaiser
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI, 96822, USA.
| | - Long Zhao
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI, 96822, USA
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
| | - Vladislav S Krasnoukhov
- Samara National Research University, Samara 443086 and Lebedev Physical Institute, 443011, Samara, Russian Federation
| | - Valeriy N Azyazov
- Samara National Research University, Samara 443086 and Lebedev Physical Institute, 443011, Samara, Russian Federation
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL, 33199, USA.
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28
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Kleimeier NF, Liu Y, Turner AM, Young LA, Chin CH, Yang T, He X, Lo JI, Cheng BM, Kaiser RI. Excited state photochemically driven surface formation of benzene from acetylene ices on Pluto and in the outer solar system. Phys Chem Chem Phys 2022; 24:1424-1436. [PMID: 34982080 DOI: 10.1039/d1cp04959c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
NASA's New Horizons mission unveiled a diverse landscape of Pluto's surface with massive regions being neutral in color, while others like Cthulhu Macula range from golden-yellow to reddish comprising up to half of Pluto's carbon budget. Here, we demonstrate in laboratory experiments merged with electronic structure calculations that the photolysis of solid acetylene - the most abundant precipitate on Pluto's surface - by low energy ultraviolet photons efficiently synthesizes benzene and polycyclic aromatic hydrocarbons via excited state photochemistry thus providing critical molecular building blocks for the colored surface material. Since low energy photons deliver doses to Pluto's surface exceeding those from cosmic rays by six orders of magnitude, these processes may significantly contribute to the coloration of Pluto's surface and of hydrocarbon-covered surfaces of Solar System bodies such as Triton in general. This discovery critically enhances our perception of the distribution of aromatic molecules and carbon throughout our Solar System.
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Affiliation(s)
- N Fabian Kleimeier
- W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA. .,Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA
| | - Yiwei Liu
- State Key Laboratory of Precision Spectroscopy, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, P. R. China.
| | - Andrew M Turner
- W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA. .,Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA
| | - Leslie A Young
- Southwest Research Institute, Department of Space Studies, Boulder, CO 80302, USA
| | - Chih-Hao Chin
- State Key Laboratory of Precision Spectroscopy, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, P. R. China.
| | - Tao Yang
- State Key Laboratory of Precision Spectroscopy, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, P. R. China. .,Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, P. R. China
| | - Xiao He
- State Key Laboratory of Precision Spectroscopy, Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, P. R. China. .,New York University - East China Normal University Center for Computational Chemistry, New York University, Shanghai 200062, P. R. China.
| | - Jen-Iu Lo
- Department of Medical Research, Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Hualien City 970, Taiwan
| | - Bing-Ming Cheng
- Department of Medical Research, Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Hualien City 970, Taiwan.,Tzu-Chi University of Science and Technology, Hualien City 970, Taiwan
| | - Ralf I Kaiser
- W. M. Keck Research Laboratory in Astrochemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA. .,Department of Chemistry, University of Hawaii at Manoa, Honolulu, HI 96822, USA
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29
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Gurusinghe RM, Dias N, Mebel AM, Suits AG. Radical-Radical Reaction Dynamics Probed Using Millimeterwave Spectroscopy: Propargyl + NH 2/ND 2. J Phys Chem Lett 2022; 13:91-97. [PMID: 34958581 DOI: 10.1021/acs.jpclett.1c03813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
We apply chirped-pulse uniform flow millimeterwave (CPUF-mmW) spectroscopy to study the complex multichannel reaction dynamics in the reaction between the propargyl and amino radicals (C3H3 + NH2/ND2), a radical-radical reaction of importance in the gas-phase chemistry of astrochemical environments and combustion systems. The photolytically generated radicals are allowed to react in a well-characterized quasi-uniform supersonic flow, and mmW rotational spectroscopy (70-93 GHz) is used for simultaneous detection of the reaction products: HCN, HNC, HC3N, DCN, DNC, and DC3N, while spectral intensities of the measured pure-rotational lines allow product branching to be quantified. High-level electronic structure calculations were used for theoretical prediction of the reaction pathways and branching. Experimentally deduced product branching fractions were compared with the results from statistical simulations based on the RRKM theory. Product branching was found to be strongly dependent on the excess internal energy of the C3H3 and NH2/ND2 reactants.
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Affiliation(s)
- Ranil M Gurusinghe
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
| | - Nureshan Dias
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Arthur G Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
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30
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Kaiser RI, Zhao L, Lu W, Ahmed M, Zagidullin MV, Azyazov VN, Mebel AM. Formation of Benzene and Naphthalene through Cyclopentadienyl-Mediated Radical-Radical Reactions. J Phys Chem Lett 2022; 13:208-213. [PMID: 34967648 DOI: 10.1021/acs.jpclett.1c03733] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Resonantly stabilized free radicals (RSFRs) have been contemplated as fundamental molecular building blocks and reactive intermediates in molecular mass growth processes leading to polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanoparticles on Earth and in deep space. By combining molecular beams and computational fluid dynamics simulations, we provide compelling evidence on the formation of benzene via the cyclopentadienyl-methyl reaction and of naphthalene through the cyclopentadienyl self-reaction, respectively. These systems offer benchmarks for the conversion of a five-membered ring to the 6π-aromatic (benzene) and the generation of the simplest 10π-PAH (naphthalene) at elevated temperatures. These results uncover molecular mass growth processes from the "bottom up" via RSFRs in high temperature circumstellar environments and combustion systems expanding our fundamental knowledge of the organic, hydrocarbon chemistry in our universe.
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Affiliation(s)
- Ralf I Kaiser
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - Long Zhao
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - Wenchao Lu
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Marsel V Zagidullin
- Lebedev Physical Institute, Samara Branch, Samara 443011, Russian Federation
| | - Valeriy N Azyazov
- Lebedev Physical Institute, Samara Branch, Samara 443011, Russian Federation
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
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31
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Couch DE, Zhang AJ, Taatjes CA, Hansen N. Experimental Observation of Hydrocarbon Growth by Resonance‐Stabilized Radical–Radical Chain Reaction. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202110929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- David E. Couch
- Gas Phase Chemical Physics Department Combustion Research Facility Sandia National Laboratories Livermore CA 94550 USA
| | - Angie J. Zhang
- Gas Phase Chemical Physics Department Combustion Research Facility Sandia National Laboratories Livermore CA 94550 USA
| | - Craig A. Taatjes
- Gas Phase Chemical Physics Department Combustion Research Facility Sandia National Laboratories Livermore CA 94550 USA
| | - Nils Hansen
- Gas Phase Chemical Physics Department Combustion Research Facility Sandia National Laboratories Livermore CA 94550 USA
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32
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Jin H, Ye L, Yang J, Jiang Y, Zhao L, Farooq A. Inception of Carbonaceous Nanostructures via Hydrogen-Abstraction Phenylacetylene-Addition Mechanism. J Am Chem Soc 2021; 143:20710-20716. [PMID: 34784469 DOI: 10.1021/jacs.1c08230] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sufficient experimental evidence has suggested that polycyclic aromatic hydrocarbons are the building blocks of carbonaceous nanostructures in combustion and circumstellar envelops of carbon-rich stars, but their fundamental formation mechanisms remain elusive. By exploring the reaction kinetics of phenylacetylene with 1-naphthyl/4-phenanthryl radicals, we provide compelling theoretical and experimental evidence for a novel and self-consistent hydrogen-abstraction phenylacetylene-addition (HAPaA) mechanism. HAPaA operates efficiently at both low and high temperatures, leading to the formation, expansion, and nucleation of peri-condensed aromatic hydrocarbons (PCAHs), which are otherwise difficult to synthesis via traditional hydrogen-abstraction acetylene/vinylacetylene-addition pathways. The HAPaA mechanism can be generalized to other α-alkynyl PCAHs and thus provides an alternative covalent bond bridge for PCAH combination via an acetylene linker. The proposed HAPaA mechanism may contribute toward a comprehensive understanding of soot formation, carbonaceous nanomaterials synthesis, and the origin and evolution of carbon in our galaxy.
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Affiliation(s)
- Hanfeng Jin
- Clean Combustion Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Lili Ye
- School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China
| | - Jiuzhong Yang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, China
| | - Yu Jiang
- Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education and Hubei Key Laboratory of Catalysis and Materials Science, Hubei R&D Center of Hyperbranched Polymers Synthesis and Applications, South-Central University for Nationalities, Wuhan 430074, China
| | - Long Zhao
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, China
| | - Aamir Farooq
- Clean Combustion Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
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33
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Puente‐Urbina A, Pan Z, Paunović V, Šot P, Hemberger P, van Bokhoven JA. Direct Evidence on the Mechanism of Methane Conversion under Non-oxidative Conditions over Iron-modified Silica: The Role of Propargyl Radicals Unveiled. Angew Chem Int Ed Engl 2021; 60:24002-24007. [PMID: 34459534 PMCID: PMC8596584 DOI: 10.1002/anie.202107553] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Indexed: 11/08/2022]
Abstract
Radical-mediated gas-phase reactions play an important role in the conversion of methane under non-oxidative conditions into olefins and aromatics over iron-modified silica catalysts. Herein, we use operando photoelectron photoion coincidence spectroscopy to disentangle the elusive C2+ radical intermediates participating in the complex gas-phase reaction network. Our experiments pinpoint different C2 -C5 radical species that allow for a stepwise growth of the hydrocarbon chains. Propargyl radicals (H2 C-C≡C-H) are identified as essential precursors for the formation of aromatics, which then contribute to the formation of heavier hydrocarbon products via hydrogen abstraction-acetylene addition routes (HACA mechanism). These results provide comprehensive mechanistic insights that are relevant for the development of methane valorization processes.
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Affiliation(s)
- Allen Puente‐Urbina
- Institute for Chemical and BioengineeringDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
| | - Zeyou Pan
- Institute for Chemical and BioengineeringDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
- Laboratory for Synchrotron Radiation and FemtochemistryPaul Scherrer InstituteForschungsstrasse 1115232VilligenSwitzerland
| | - Vladimir Paunović
- Institute for Chemical and BioengineeringDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
| | - Petr Šot
- Institute for Chemical and BioengineeringDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
- Laboratory of Inorganic ChemistryDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and FemtochemistryPaul Scherrer InstituteForschungsstrasse 1115232VilligenSwitzerland
| | - Jeroen Anton van Bokhoven
- Institute for Chemical and BioengineeringDepartment of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 1–5/108093ZurichSwitzerland
- Laboratory for Catalysis and Sustainable ChemistryPaul Scherrer InstituteForschungsstrasse 1115232VilligenSwitzerland
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34
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Puente‐Urbina A, Pan Z, Paunović V, Šot P, Hemberger P, Bokhoven JA. Direct Evidence on the Mechanism of Methane Conversion under Non‐oxidative Conditions over Iron‐modified Silica: The Role of Propargyl Radicals Unveiled. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202107553] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Allen Puente‐Urbina
- Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
| | - Zeyou Pan
- Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
- Laboratory for Synchrotron Radiation and Femtochemistry Paul Scherrer Institute Forschungsstrasse 111 5232 Villigen Switzerland
| | - Vladimir Paunović
- Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
| | - Petr Šot
- Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
- Laboratory of Inorganic Chemistry Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
| | - Patrick Hemberger
- Laboratory for Synchrotron Radiation and Femtochemistry Paul Scherrer Institute Forschungsstrasse 111 5232 Villigen Switzerland
| | - Jeroen Anton Bokhoven
- Institute for Chemical and Bioengineering Department of Chemistry and Applied Biosciences ETH Zurich Vladimir-Prelog-Weg 1–5/10 8093 Zurich Switzerland
- Laboratory for Catalysis and Sustainable Chemistry Paul Scherrer Institute Forschungsstrasse 111 5232 Villigen Switzerland
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Ross SD, Flores J, Khani S, Hewett DM, Reilly NJ. Optical Identification of the Resonance-Stabilized para-Ethynylbenzyl Radical. J Phys Chem A 2021; 125:9115-9127. [PMID: 34614356 DOI: 10.1021/acs.jpca.1c07039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We report the spectroscopic observation of the jet-cooled para-ethynylbenzyl (PEB) radical, a resonance-stabilized isomer of C9H7. The radical was produced in a discharge of p-ethynyltoluene diluted in argon and probed by resonant two-color two-photon ionization (R2C2PI) spectroscopy. The origin of the D0(2B1)-D1(2B1) transition of PEB appears at 19,506 cm-1. A resonant two-color ion-yield scan reveals an adiabatic ionization energy (AIE) of 7.177(1) eV, which is almost symmetrically bracketed by CBS-QB3 and B3LYP/6-311G++(d,p) calculations. The electronic spectrum exhibits pervasive Fermi resonances, in that most a1 fundamentals are accompanied by similarly intense overtones or combination bands of non-totally symmetric modes that would carry little intensity in the harmonic approximation. Under the same experimental conditions, the m/z = 115 R2C2PI spectrum of the p-ethynyltoluene discharge also exhibits contributions from the m-ethynylbenzyl and 1-phenylpropargyl radicals. The former, like PEB, is observed herein for the first time, and its identity is confirmed by measurement and calculation of its AIE and D0-D1 origin transition energy; the latter is identified by comparison with its known electronic spectrum (J. Am. Chem. Soc., 2008, 130, 3137-3142). Both species are found to co-exist with PEB at levels vastly greater than might be explained by any precursor sample impurity, implying that interconversion of ethynylbenzyl motifs is feasible in energetic environments such as plasmas and flames, wherein resonance-stabilized radicals are persistent.
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Affiliation(s)
- Sederra D Ross
- 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
| | - Sima Khani
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
| | - Daniel M Hewett
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
| | - Neil J Reilly
- Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
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Couch DE, Zhang AJ, Taatjes CA, Hansen N. Experimental Observation of Hydrocarbon Growth by Resonance-Stabilized Radical-Radical Chain Reaction. Angew Chem Int Ed Engl 2021; 60:27230-27235. [PMID: 34605134 DOI: 10.1002/anie.202110929] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Indexed: 01/08/2023]
Abstract
Rapid molecular-weight growth of hydrocarbons occurs in flames, in industrial synthesis, and potentially in cold astrochemical environments. A variety of high- and low-temperature chemical mechanisms have been proposed and confirmed, but more facile pathways may be needed to explain observations. We provide laboratory confirmation in a controlled pyrolysis environment of a recently proposed mechanism, radical-radical chain reactions of resonance-stabilized species. The recombination reaction of phenyl (c-C6 H5 ) and benzyl (c-C6 H5 CH2 ) radicals produces both diphenylmethane and diphenylmethyl radicals, the concentration of the latter increasing with rising temperature. A second phenyl addition to the product radical forms both triphenylmethane and triphenylmethyl radicals, confirming the propagation of radical-radical chain reactions under the experimental conditions of high temperature (1100-1600 K) and low pressure (ca. 3 kPa). Similar chain reactions may contribute to particle growth in flames, the interstellar medium, and industrial reactors.
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Affiliation(s)
- David E Couch
- Gas Phase Chemical Physics Department, Combustion Research Facility, Sandia National Laboratories, Livermore, CA, 94550, USA
| | - Angie J Zhang
- Gas Phase Chemical Physics Department, Combustion Research Facility, Sandia National Laboratories, Livermore, CA, 94550, USA
| | - Craig A Taatjes
- Gas Phase Chemical Physics Department, Combustion Research Facility, Sandia National Laboratories, Livermore, CA, 94550, USA
| | - Nils Hansen
- Gas Phase Chemical Physics Department, Combustion Research Facility, Sandia National Laboratories, Livermore, CA, 94550, USA
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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: 8] [Impact Index Per Article: 2.0] [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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The Effect of Cluster Size on the Intra-Cluster Ionic Polymerization Process. Molecules 2021; 26:molecules26164782. [PMID: 34443370 PMCID: PMC8399435 DOI: 10.3390/molecules26164782] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 08/02/2021] [Accepted: 08/04/2021] [Indexed: 11/17/2022] Open
Abstract
Polyaromatic hydrocarbons (PAHs) are widespread in the interstellar medium (ISM). The abundance and relevance of PAHs call for a clear understanding of their formation mechanisms, which, to date, have not been completely deciphered. Of particular interest is the formation of benzene, the basic building block of PAHs. It has been shown that the ionization of neutral clusters can lead to an intra-cluster ionic polymerization process that results in molecular growth. Ab-initio molecular dynamics (AIMD) studies in clusters consisting of 3-6 units of acetylene modeling ionization events under ISM conditions have shown maximum aggregation of three acetylene molecules forming bonded C6H6+ species; the larger the number of acetylene molecules, the higher the production of C6H6+. These results lead to the question of whether clusters larger than those studied thus far promote aggregation beyond three acetylene units and whether larger clusters can result in higher C6H6+ production. In this study, we report results from AIMD simulations modeling the ionization of 10 and 20 acetylene clusters. The simulations show aggregation of up to four acetylene units producing bonded C8H8+. Interestingly, C8H8+ bicyclic species were identified, setting a precedent for their astrochemical identification. Comparable reactivity rates were shown with 10 and 20 acetylene clusters.
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