Kinetics of CH Radicals With O2: Evidence for CO-Chemiluminescence in the Gas Phase Reaction

Vaghjiani, Ghanshyam L.

doi:10.21236/ada406218

Cited by 4 publications

(4 citation statements)

References 5 publications

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“…The reactions occur inside a quartz tube at 4 Torr (533 Pa) and 298 K. The gas flow consists of small amounts of the CH radical precursor and acrolein in a large excess of helium buffer gas with around 15% nitrogen. Bromoform (CHBr 3 or deuterated bromoform CDBr 3 ) is used as the radical precursor and the laser dissociation of CHBr 3 is an effective method to produce CH radicals with high yield. ,− Liquid bromoform is placed in a glass vessel and kept at a temperature of 8 °C. Helium is bubbled through the liquid at a total pressure of 700 Torr, entraining bromoform in the flow.…”

Section: Methodsmentioning

confidence: 99%

Isomer Specific Product Detection in the Reaction of CH with Acrolein

et al. 2013

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The products formed in the reaction between the methylidene radical (CH) and acrolein (CH2═CHCHO) are probed at 4 Torr and 298 K employing tunable vacuum-ultraviolet synchrotron light and multiplexed photoionization mass-spectrometry. The data suggest a principal exit channel of H loss from the adduct to yield C4H4O, accounting for (78 ± 10)% of the products. Examination of the photoionization spectra measured upon reaction of both CH and CD with acrolein reveals that the isomeric composition of the C4H4O product is (60 ± 12)% 1,3-butadienal and (17 ± 10)% furan. The remaining 23% of the possible C4H4O products cannot be accurately distinguished without more reliable photoionization spectra of the possible product isomers but most likely involves oxygenated butyne species. In addition, C2H2O and C3H4 are detected, which account for (14 ± 10)% and (8 +10, -8)% of the products, respectively. The C2H2O photoionization spectrum matches that of ketene and the C3H4 signal is composed of (24 ± 14)% allene and (76 ± 22)% propyne, with an upper limit of 8% placed on the cyclopropene contribution. The reactive potential energy surface is also investigated computationally, and specific rate coefficients are calculated with RRKM theory. These calculations predict overall branching fractions for 1,3-butadienal and furan of 27% and 12%, respectively, in agreement with the experimental results. In contrast, the calculations predict a prominent CO + 2-methylvinyl product channel that is at most a minor channel according to the experimental results. Studies with the CD radical strongly suggest that the title reaction proceeds predominantly via cycloaddition of the radical onto the C═O bond of acrolein, with cycloaddition to the C═C bond being the second most probable reactive mechanism.

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Section: Methodsmentioning

confidence: 99%

Isomer Specific Product Detection in the Reaction of CH with Acrolein

et al. 2013

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“…The photolysis of CHBr 3 at 266 nm is likely to produce some excited state CH(a 4 ) radicals in our experiments which might interfere with our investigation of the kinetics of the CH(X 2 Π r ) + H 2 O reaction. It has been estimated29 that the photolysis of CHBr 3 at 248 nm produces five times more CH radicals in the X 2 Π r state than in the a 4  state. Consequently we expect that there will be a slightly smaller relative yield of CH(a 4 ) at 266 nm given the lower energy available.…”

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confidence: 99%

Unusual Low-Temperature Reactivity of Water: The CH + H₂O Reaction as a Source of Interstellar Formaldehyde?

Hickson

Loison

Caubet

2013

J. Phys. Chem. Lett.

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Water is an important reservoir species for oxygen in interstellar space and plays a key role in the physics of star formation through cooling by far-infrared emission. Whilst water vapour is present at high abundances in the outflows of protostars, its contribution to the chemical evolution of these regions is a minor one due to its limited low temperature reactivity in the gasphase. Here, we performed kinetic experiments on the barrierless CH + H 2 O reaction in a supersonic flow reactor down to 50 K. The measured rate increases rapidly below room temperature, confirming and extending the predictions of earlier statistical calculations. The open Corresponding Author

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“…The multiphoton photodissociation of CBr 4 at 248 nm eliminates multiple halogen atoms, leading to the formation of carbon atoms 62 and CBr radicals. 63,64 Under our experimental conditions 20% of the introduced CBr 4 is photodissociated. Shannon et al 63 determined a C( 1 D)/C( 3 P) ratio following CBr 4 photodissocation at 266 nm of 0.15 ± 0.04 at 296 K. Molecular nitrogen is known to efficiently quench C( 1 D) atoms through C( 1 D) + N 2 → C( 3 P) + N 2 with a reaction rate coefficient of k = 5.3 × 10 −12 cm 3 molecules −1 s −1 .…”

Section: Experimetal Proceduresmentioning

confidence: 89%

Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments

et al. 2016

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Product detection studies of C(P) atom reactions with butene (CH) isomers (but-1-ene, cis-but-2-ene, trans-but-2-ene) are carried out in a flow tube reactor at 353 K and 4 Torr under multiple collision conditions. Ground state carbon atoms are generated by 248 nm laser photolysis of tetrabromomethane, CBr, in a buffer of helium. Thermalized reaction products are detected using synchrotron tunable VUV photoionization and time-of-flight mass spectrometry. The temporal profiles of the detected ions are used to discriminate products from side or secondary reactions. For the C(P) + trans-but-2-ene and C(P) + cis-but-2-ene reactions, various isomers of CH and CH are identified as reaction products formed via CH and H elimination. Assuming equal ionization cross sections for all CH and CH isomers, CH:CH branching ratios of 0.63:1 and 0.60:1 are derived for the C(P) + trans-but-2-ene and the C(P) + cis-but-2-ene reactions, respectively. For the C(P) + but-1-ene reaction, two reaction channels are observed: the H-elimination channel, leading to the formation of the ethylpropargyl isomer, and the CH + CH channel. Assuming equal ionization cross sections for ethylpropargyl and CH radicals, a branching ratio of 1:0.95 for the CH + CH and H + ethylpropargyl channels is derived. The experimental results are compared to previous H atom branching ratios and used to propose the most likely mechanisms for the reaction of ground state carbon atoms with butene isomers.

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Kinetics of CH Radicals With O2: Evidence for CO-Chemiluminescence in the Gas Phase Reaction

Cited by 4 publications

References 5 publications

Isomer Specific Product Detection in the Reaction of CH with Acrolein

Isomer Specific Product Detection in the Reaction of CH with Acrolein

Unusual Low-Temperature Reactivity of Water: The CH + H₂O Reaction as a Source of Interstellar Formaldehyde?

Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments

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Kinetics of CH Radicals With O2: Evidence for CO-Chemiluminescence in the Gas Phase Reaction

Cited by 4 publications

References 5 publications

Isomer Specific Product Detection in the Reaction of CH with Acrolein

Isomer Specific Product Detection in the Reaction of CH with Acrolein

Unusual Low-Temperature Reactivity of Water: The CH + H2O Reaction as a Source of Interstellar Formaldehyde?

Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments

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Unusual Low-Temperature Reactivity of Water: The CH + H₂O Reaction as a Source of Interstellar Formaldehyde?