Ab initio study of the structures and properties of isomeric hydrocarbon radical species, C4H3

Ha, Tae–Kyu; Gey, E.

doi:10.1016/0166-1280(94)80040-5

Cited by 10 publications

(7 citation statements)

References 11 publications

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“…Calculated heats of formation (0 K) of various neutral isomers of C 4 H 3 are shown in Table and compared to literature values. The acyclic vinylethynyl radical (H 2 CCHC⋮C • ) is found to be less stable, as are the cyclic radicals derived from cyclobutadiene ( cyclic -C 4 H 3 ) or exo -methylene cyclopropene (−C(CH)CHCH−) 1 Heats of Formation of Different C 4 H 3 Isomers Δ f H ° (0 K) (kcal mol -1 )speciesHL b literature c Q1 diag.…”

Section: Resultsmentioning

confidence: 99%

Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

et al. 2006

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Quantitative identification of isomers of hydrocarbon radicals in flames is critical to understanding soot formation. Isomers of C4H3 and C4H5 in flames fueled by allene, propyne, cyclopentene, or benzene are identified by comparison of the observed photoionization efficiencies with theoretical simulations based on calculated ionization energies and Franck-Condon factors. The experiments combine molecular-beam mass spectrometry (MBMS) with photoionization by tunable vacuum-ultraviolet synchrotron radiation. The theoretical simulations employ the rovibrational properties obtained with B3LYP/6-311++G(d,p) density functional theory and electronic energies obtained from QCISD(T) ab initio calculations extrapolated to the complete basis set limit. For C4H3, the comparisons reveal the presence of the resonantly stabilized CH2CCCH isomer (i-C4H3). For C4H5, contributions from the CH2CHCCH2 (i-C4H5) and some combination of the CH3CCCH2 and CH3CHCCH isomers are evident. Quantitative concentration estimates for these species are made for allene, cyclopentene, and benzene flames. Because of low Franck-Condon factors, sensitivity to n-isomers of both C4H3 and C4H5 is limited. Adiabatic ionization energies, as obtained from fits of the theoretical predictions to the experimental photoionization efficiency curves, are within the error bars of the QCISD(T) calculations. For i-C4H3 and i-C4H5, these fitted adiabatic ionization energies are (8.06 +/- 0.05) eV and (7.60 +/- 0.05) eV, respectively. The good agreement between the fitted and theoretical ionization thresholds suggests that the corresponding theoretically predicted radical heats of formation (119.1, 76.3, 78.7, and 79.1 kcal/mol at 0 K for i-C4H3, i-C4H5, CH3CCCH2, and CH3CHCCH, respectively) are also quite accurate.

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Section: Resultsmentioning

confidence: 99%

Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

et al. 2006

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“…An ab initio study of the structures and properties of the free radical C 4 H 3 was completed by Ha and Gey . Two low-lying isomers 2-dehydro-buta-1-ene-3-yne (iso-C 4 H 3 ) and 1-dehydro-buta-1-ene-3-yne ( n -C 4 H 3 ) were found to be the most stable. − Miller et al noted that iso-C 4 H 3 is thermodynamically more stable (9.6 kcal/mol) than n -C 4 H 3 , and thus most of the C 4 H 3 should be in the form of the iso isomer even at combustion temperatures . It seems likely that the C 4 H 3 fragment from photodissociation of thiophene survives also as the iso-C 4 H 3 isomer (HC⋮C−CCH 2 ).…”

Section: Resultsmentioning

confidence: 99%

193 nm Photodissociation of Thiophene Probed Using Synchrotron Radiation

Sorkhabi

Rizvi

et al. 1999

J. Phys. Chem. A

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The photodissociation dynamics of thiophene, c-C4H4S, have been studied at 193 nm using tunable synchrotron undulator radiation as a universal product probe. Five primary dissociation channels have been observed, and the translational energy distributions and photoionization efficiency spectra have been recorded for all products. The evidence suggests that dissociation occurs on the ground-state surface following internal conversion.

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“…Most of the topologically possible structures of these species were calculated, although we could not exclude that some other higher energy isomers may exist. The geometries of various isomers of the doublet C 4 H 3 (most of the structures reported here were calculated earlier by us31 and in the literature33), transition states for isomerization and dissociation, as well as the C 4 H 2 dissociation products were optimized using the hybrid density functional B3LYP method34 with the 6‐311G(d,p) basis set 35. Vibrational frequencies calculated at the same level were used for characterization of stationary points and zero‐point energy (ZPE) correction without scaling.…”

Section: Methodsmentioning

confidence: 99%

Ab initio study of C₄H₃ potential energy surface and reaction of ground‐state carbon atom with propargyl radical

Mebel

Kaiser

2001

J Comput Chem

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The potential energy surface for the reaction of the ground-state carbon atom [C( 3 P j )] with the propargyl radical [HCCCH 2 (X 2 B 1 )] is investigated using the G2M(RCC,MP2) method. Numerous local minima and transition states for various isomerization and dissociation pathways of doublet C 4 H 3 are studied. The results show that C( 3 P j ) attacks the π system of the propargyl radical at the acetylenic carbon atom and yields the n-C 4 H 3 ( 2 A ) isomer i3 after an 1,2-H atom shift. This intermediate either splits a hydrogen atom and produces singlet diacetylene, [HCCCCH (p1) + H] or undergoes (to a minor amount) a 1,2-H migration to i-C 4 H 3 ( 2 A ) i5, which in turn dissociates to p1 plus an H atom. Alternatively, atomic carbon adds to the triple C≡C bond of the propargyl radical to form a three-member ring C 4 H 3 isomer i1, which ring opens to i3. Diacetylene is concluded to be a nearly exclusive product of the C( 3 P j ) + HCCCH 2 reaction. At the internal energy of 10.0 kcal/mol above the reactant level, Rice-Ramsperger-Kassel-Marcus calculations show about 91.7% of HCCCCH comes from fragmentation of i3 and 8.3% from i5. The other possible minor channels are identified as HCCCC + H 2 and C 2 H + HCCH.

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Ab initio study of the structures and properties of isomeric hydrocarbon radical species, C4H3

Cited by 10 publications

References 11 publications

Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

193 nm Photodissociation of Thiophene Probed Using Synchrotron Radiation

Ab initio study of C₄H₃ potential energy surface and reaction of ground‐state carbon atom with propargyl radical

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Ab initio study of the structures and properties of isomeric hydrocarbon radical species, C4H3

Cited by 10 publications

References 11 publications

Identification and Chemistry of C4H3 and C4H5 Isomers in Fuel-Rich Flames

Identification and Chemistry of C4H3 and C4H5 Isomers in Fuel-Rich Flames

193 nm Photodissociation of Thiophene Probed Using Synchrotron Radiation

Ab initio study of C4H3 potential energy surface and reaction of ground‐state carbon atom with propargyl radical

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Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

Identification and Chemistry of C₄H₃ and C₄H₅ Isomers in Fuel-Rich Flames

Ab initio study of C₄H₃ potential energy surface and reaction of ground‐state carbon atom with propargyl radical