Identification and chemistry of C4H3 and C4H5 isomers in fuel-rich flames
| Autor: | Lixia Wei, Bin Yang, Craig A. Taatjes, Stephen J. Klippenstein, Juan Wang, T.A. Cool, Fei Qi, Rui Yang, Matthew E. Law, Chaoqun Huang, Jing Wang, Nils Hansen, Phillip R. Westmoreland, James A. Miller |
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| Rok vydání: | 2006 |
| Předmět: |
Chemical Phenomena
Molecular Structure Chemistry Pyridines Carbon Compounds Inorganic Analytical chemistry Rotational–vibrational spectroscopy Photoionization Propyne Mass spectrometry Mass Spectrometry chemistry.chemical_compound Isomerism Soot Ab initio quantum chemistry methods Spectrometry Mass Matrix-Assisted Laser Desorption-Ionization Physics::Atomic and Molecular Clusters Density functional theory Gases Physics::Chemical Physics Physical and Theoretical Chemistry Ionization energy Protons Basis set |
| Zdroj: | The journal of physical chemistry. A. 110(10) |
| ISSN: | 1089-5639 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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