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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Identification of C_5H_x Isomers in Fuel-Rich Flames by Photoionization Mass Spectrometry and Electronic Structure Calculations
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Identification of C_5H_x Isomers in Fuel-Rich Flames by Photoionization Mass Spectrometry and Electronic Structure Calculations

机译：通过光电离质谱法和电子结构计算鉴定富燃料火焰中的C_5H_x异构体

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摘要

The isomeric composition of C_5H_X (x=2-6,8)flame species is analyzed for rich flames fueled by allene,propyne,cyclopentene,or benzene.Different isomers are identified by their known ionization energies and/or by comparison of the observed photoionization efficiencies with theoretical simulations based on calculated ionization energies and Franck-Condon factors.The experiments combine flame-sampling molecular-beam mass spectrometry with photoionization by tunable vacuum-UV 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)electronic structure calculations extrapolated to the complete basis set limit.For C5H3,the comparison reveals the presence of both the H_2CCCCCH (i-C_5H_3)and the HCCCHCCH (n-C_5H_3)isomer.The simulations also suggest a modest amount of cyclo-CCHCHCCH-,which is consistent with a minor signal for C_5H_2 that is apparently due to cvclo-CCHCCCH-.For C_5H_4,contributions from the CH_2CCCCH_2 (1,2,3,4-pentatetraene),CH_2CCHCCH,and CH_3CCCCH (1,3-pentadiyne)isomers are evident,as is some contribution from CHCCH_2CCH (1,4-pentadiyne)in the cyclopentene and benzene flames.Signal at m/z = 65 originates mainly from the cyclopentadienyl radical.For C_5H_6,contributions from cyclopentadiene,CH_3CCCHCH_2,CH_3CHCHCCH,and CH_2CHCH_2CCH are observed.No signal is observed for C_5H_7 species.Cyclopentene,CH_2CHCHCHCH_3 (1,3-pentadiene),CH_3CCCH_2CH_3 (2-pentyne),and CH_2-CHCH_2CHCH_2 (1,4-pentadiene)contribute to the signal at m/z = 68.Newly derived ionization energies for i-and n-C_5H_3 (8.20 +-0.05 and 8.31 +-0.05 eV,respectively),CH_2CCHCCH (9.22 +-0.05 eV),and CH_2-CHCH_2CCH (9.95 +-0.05 eV)are within the error bars of the QCISD(T)calculations.The combustion chemistry of the observed C_5H_x intermediates and the impact on flame chemistry models are discussed.
机译：分析了C_5H_X（x = 2-6,8）火焰物种的异构体组成，以分析丙二烯，丙炔，环戊烯或苯燃烧产生的浓火焰，通过其已知的电离能和/或通过比较观察到的光电离来鉴定不同的异构体基于计算的电离能和Franck-Condon因子的理论模拟的效率。该实验将火焰采样分子束质谱与可调谐真空-UV同步加速器辐射的光电离结合在一起。理论模拟利用了B3LYP / 6-311获得的旋转振动特性。从QCISD（T）电子结构计算获得的++ G（d，p）密度泛函理论和电子能量推算到完整的基集极限。对于C5H3，比较显示H_2CCCCCH（i-C_5H_3）和HCCCHCCH（n-C_5H_3）异构体。模拟还表明环CCHCHCCHCH-的量适中，这与C_5H_2的次要信号相一致，这显然是由于cvclo-CCHCCCH-。对于C_5H_4，来自CH_2CCCCH_2（1,2,3,4-戊二烯），CH_2CCHCCH和CH_3CCCCH（1,3-戊二炔）异构体的贡献很明显，来自CHCCH_2CCH（1,4-在m / z = 65处的信号主要来自环戊二烯基。对于C_5H_6，观察到来自环戊二烯，CH_3CCCHCH_2，CH_3CHCHCCH和CH_2CHCH_2CCH的贡献。对于C_5H_CH_2物种未观察到信号。 （1,3-戊二烯），CH_3CCCH_2CH_3（2-戊炔）和CH_2-CHCH_2CHCH_2（1,4-戊二烯）贡献于m / z = 68的信号.i和n-C_5H_3的新电离能（8.20分别为+ -0.05和8.31 + -0.05 eV，CH_2CCHCCH（9.22 + -0.05 eV）和CH_2-CHCH_2CCH（9.95 + -0.05 eV）均在QCISD（T）计算的误差栏中。讨论了观察到的C_5H_x中间体及其对火焰化学模型的影响。

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