From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene
© 2019 the Owner Societies. Hydrogen-abstraction-C2H2-addition (HACA) is one of the most important pathways leading to the formation of naphthalene, the simplest two-ring polycyclic aromatic hydrocarbon (PAH). The major reaction channels for naphthalene formation have previously been calculated by M...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Royal Society of Chemistry (RSC)
2021
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| Online Access: | https://hdl.handle.net/1721.1/136473 |
| _version_ | 1811090247399768064 |
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| author | Chu, Te-Chun Buras, Zachary J Smith, Mica C Uwagwu, Awele B Green, William H |
| author_facet | Chu, Te-Chun Buras, Zachary J Smith, Mica C Uwagwu, Awele B Green, William H |
| author_sort | Chu, Te-Chun |
| collection | MIT |
| description | © 2019 the Owner Societies. Hydrogen-abstraction-C2H2-addition (HACA) is one of the most important pathways leading to the formation of naphthalene, the simplest two-ring polycyclic aromatic hydrocarbon (PAH). The major reaction channels for naphthalene formation have previously been calculated by Mebel et al., but few experiments exist to validate the theoretical predictions. In this work, time-resolved molecular beam mass spectrometry (MBMS) was used to investigate the time-dependent product formation in the reaction of a phenyl radical with C2H2 for the first time, at temperatures of 600 and 700 K and pressures of 10 and 50 Torr. A pressure-dependent model was developed with rate parameters derived from Mebel et al.'s calculations and from newly calculated pathways on the C8H7 PES at the G3(MP2,CC)//B3LYP/6-311G∗∗ level of theory. The model prediction is consistent with the MBMS product profiles at a mass-to-charge ratio (m/z) of 102 (corresponding to the H-loss product from C8H7, phenylacetylene), 103 (the initial C8H7 adduct and its isomers plus the 13C isotopologue of phenylacetylene), 128 (naphthalene), and 129 (C10H9 isomers plus the 13C isotopologue of naphthalene). An additional C8H7 isomer, bicyclo[4.2.0]octa-1,3,5-trien-7-yl, not considered by Mebel et al.'s calculations, contributes significantly to the signal at m/z 103 due to its stable energy and low reactivity. At high C2H2 concentrations, bimolecular reactions dominated the observed chemistry, and the m/z 128 and m/z 102 MBMS signal ratio was measured to directly determine the product branching ratio. At 600 K and 10 Torr, branching to the H-loss product (phenylacetylene) on the C8H7 PES accounted for 7.9% of phenyl radical consumption, increasing to 15.9% at 700 K and 10 Torr. At 50 Torr, the branching was measured to be 2.8% at 600 K and 6.2% at 700 K. Adduct stabilization is favored at higher pressure and lower temperature, which hinders the formation of the H-loss product. The pressure-dependent model predicted the observed branching ratios within the experimental uncertainty, indicating that the rate parameters reported here can be used in combustion mechanisms to provide insights into phenyl HACA reactions and PAH formation. |
| first_indexed | 2024-09-23T14:39:49Z |
| format | Article |
| id | mit-1721.1/136473 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T14:39:49Z |
| publishDate | 2021 |
| publisher | Royal Society of Chemistry (RSC) |
| record_format | dspace |
| spelling | mit-1721.1/1364732022-03-29T20:51:33Z From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene Chu, Te-Chun Buras, Zachary J Smith, Mica C Uwagwu, Awele B Green, William H © 2019 the Owner Societies. Hydrogen-abstraction-C2H2-addition (HACA) is one of the most important pathways leading to the formation of naphthalene, the simplest two-ring polycyclic aromatic hydrocarbon (PAH). The major reaction channels for naphthalene formation have previously been calculated by Mebel et al., but few experiments exist to validate the theoretical predictions. In this work, time-resolved molecular beam mass spectrometry (MBMS) was used to investigate the time-dependent product formation in the reaction of a phenyl radical with C2H2 for the first time, at temperatures of 600 and 700 K and pressures of 10 and 50 Torr. A pressure-dependent model was developed with rate parameters derived from Mebel et al.'s calculations and from newly calculated pathways on the C8H7 PES at the G3(MP2,CC)//B3LYP/6-311G∗∗ level of theory. The model prediction is consistent with the MBMS product profiles at a mass-to-charge ratio (m/z) of 102 (corresponding to the H-loss product from C8H7, phenylacetylene), 103 (the initial C8H7 adduct and its isomers plus the 13C isotopologue of phenylacetylene), 128 (naphthalene), and 129 (C10H9 isomers plus the 13C isotopologue of naphthalene). An additional C8H7 isomer, bicyclo[4.2.0]octa-1,3,5-trien-7-yl, not considered by Mebel et al.'s calculations, contributes significantly to the signal at m/z 103 due to its stable energy and low reactivity. At high C2H2 concentrations, bimolecular reactions dominated the observed chemistry, and the m/z 128 and m/z 102 MBMS signal ratio was measured to directly determine the product branching ratio. At 600 K and 10 Torr, branching to the H-loss product (phenylacetylene) on the C8H7 PES accounted for 7.9% of phenyl radical consumption, increasing to 15.9% at 700 K and 10 Torr. At 50 Torr, the branching was measured to be 2.8% at 600 K and 6.2% at 700 K. Adduct stabilization is favored at higher pressure and lower temperature, which hinders the formation of the H-loss product. The pressure-dependent model predicted the observed branching ratios within the experimental uncertainty, indicating that the rate parameters reported here can be used in combustion mechanisms to provide insights into phenyl HACA reactions and PAH formation. 2021-10-27T20:35:34Z 2021-10-27T20:35:34Z 2019 2019-10-29T12:46:43Z Article http://purl.org/eprint/type/JournalArticle https://hdl.handle.net/1721.1/136473 en 10.1039/c9cp04554f Physical Chemistry Chemical Physics Creative Commons Attribution 3.0 unported license https://creativecommons.org/licenses/by/3.0/ application/pdf Royal Society of Chemistry (RSC) Royal Society of Chemistry (RSC) |
| spellingShingle | Chu, Te-Chun Buras, Zachary J Smith, Mica C Uwagwu, Awele B Green, William H From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title | From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title_full | From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title_fullStr | From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title_full_unstemmed | From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title_short | From benzene to naphthalene: direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| title_sort | from benzene to naphthalene direct measurement of reactions and intermediates of phenyl radicals and acetylene |
| url | https://hdl.handle.net/1721.1/136473 |
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