低激发态CN自由基光谱参数的理论研究
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摘要
CN自由基在碳化物的燃烧过程中一直扮演着重要的角色。采用量化计算方法对CN自由基进行了从头计算。首先利用Hartree-Fock自洽场方法进行轨道计算,再使用完全活性空间自洽场对轨道进行优化,然后采用多参考组态相互作用的方法计算了在0.06到0.7 nm的核间距范围内CN自由基3个低激发态(X~2Σ~+,A~2Π和B~2Σ~+)的势能曲线。为了进一步提高计算的精度,考虑相对论效应选择aug-cc-pV5Z-dk相关一致基组。求解径向薛定谔方程,得到了各电子态振-转能级的能量和振-转常数,并拟合获得这些电子态的光谱常数(T_e,R_e,ω_e,ω_eχ_e,B_e,α_e)及Franck-Condon因子,其与实验结果基本一致。同时,计算CN自由基A~2∏-X~2∑~+的跃迁偶极矩,并得到5个低振动能级的辐射寿命τ和振子强度f_(00)。计算获得辐射寿命为～4μs,与实验测量结果符合较好,为研究燃烧过程中动力学行为提供了理论依据。
CN radical plays an important role in the combustion of carbides.The low-excited state of CN was investigated by the ab initio calculation.Firstly,the molecular orbitals were determined by the Hartree-Fock self-consistent field approximation and optimized to use the complete active space self-consistent field theory.Then,the potential energy curves of three low excited states(X~2Σ~+,A~2Π,and B~2Σ~+) for CN in the range of nuclear distance from 0.06 to 0.7 nm were obtained through multi-reference configuration interaction method.Considering the relativistic effects,the aug-cc-pV5 Z-dk correlation-consistent basis set was selected in order to further improve the accuracy of the calculation.The vibration-rotation energy and constants of these electronic states were derived via solving the Schrodinger equation.Through fitting date listed above,the spectral constants(T_e,R_e,ω_e,ω_eχ_e,B_e,α_e),which are basically consistent with the experimental results,and Franck-Condon factors of three low excited states were acquired.Simultaneously,the transition dipole moments of the A~2Π-X~2Σ~+ electric transition of CN have been computed,deducing the radiation lifetime τ and the oscillator strength f_(00) of the five low vibration levels.The calculated radiation lifetime is approximately 4 μs in accordance with the experimental measurements,which helps the study of the combustion dynamic.
CN radical plays an important role in the combustion of carbides.The low-excited state of CN was investigated by the ab initio calculation.Firstly,the molecular orbitals were determined by the Hartree-Fock self-consistent field approximation and optimized to use the complete active space self-consistent field theory.Then,the potential energy curves of three low excited states(X~2Σ~+,A~2Π,and B~2Σ~+) for CN in the range of nuclear distance from 0.06 to 0.7 nm were obtained through multi-reference configuration interaction method.Considering the relativistic effects,the aug-cc-pV5 Z-dk correlation-consistent basis set was selected in order to further improve the accuracy of the calculation.The vibration-rotation energy and constants of these electronic states were derived via solving the Schrodinger equation.Through fitting date listed above,the spectral constants(T_e,R_e,ω_e,ω_eχ_e,B_e,α_e),which are basically consistent with the experimental results,and Franck-Condon factors of three low excited states were acquired.Simultaneously,the transition dipole moments of the A~2Π-X~2Σ~+ electric transition of CN have been computed,deducing the radiation lifetime τ and the oscillator strength f_(00) of the five low vibration levels.The calculated radiation lifetime is approximately 4 μs in accordance with the experimental measurements,which helps the study of the combustion dynamic.
引文
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[15] Bose D J,Wright M W,Bogdanoff D,et al.Modeling and Experimental Assessment of CN Radiation Behind a Strong Shock Wave[J].Journal of Thermophysics and Heat Transfer,2006,20(2):220-230.doi:10.2514/1.16869.
[16] YIN Y,SHI D H,SUN J F,et al.Transition Dipole Moments and Transition Probabilities of the CN Radical[J].The Astrophysical Journal Supplement Series,2018,235(2):25.doi:10.3847/1538-4365/aab26b.
[17] Huber K P,Herzberg G.Molecular Spectra and Molecular Structure Ⅳ:Constants of Diatomic Molecules[M].Princeton:Van Nostrand Reinhold Company,1979.
[18] Duric N,Erman P,Larsson M.The Influence of Collisional Transfers and Perturbations on Measured A and B State Lifetimes in CN[J].Physica Scripta,1978,18(1):39-46.doi:10.1088/0031-8949/18/1/012.
[19] 王利东,李萍,张昌华,等.正癸烷燃烧反应中OH,CH和C2自由基的瞬态发射光谱[J].光谱学与光谱分析,2012,32(5):1166-1169.doi:10.3964/j.issn.1000-0593(2012)05-1166-04.
[20] 谈宁馨,王静波,华晓筱,等.甲基环己烷的高温燃烧机理及动力学模拟[J].高等学校化学学报,2011,32(8):1832-1837.doi:0251-0790(2011)08-1832-06.
[21] 姚倩,彭莉娟,李泽荣,等.烷烃与氢过氧自由基氢提取反应类反应能垒与速率常数的精确计算[J].物理化学学报,2017,33(4):763-768.doi:10.3866/PKU.WHXB201701091.
[22] Lewandowski H J,Hudson E R,Bochinski J R,et al.A Pulsed,Low-temperature Beam of Supersonically Cooled Free Radical OH Molecules[J].Chemical Physics Letters,2004,395(1-3):53-57.doi:10.1016/j.cplett.2004.07.050.
[2] 许保恩,李晓艳,曾艳丽,等.CH3SH与CN·自由基的反应机理及电子密度拓扑分析[J].物理化学学报,2008,24(7):1245-1251.doi:10.3866/PKU.WHXB20080721.
[3] Daugey N,Bergeat A,Loison J C,et al.CN (A2Πi → X2Σ+) Chemiluminescence from the N+C2N,N+CCl,and N+C2 Reactions Under Low-pressure Fast-flow Conditions[J].Chemical Physics Letters,2000,324(1-3):1-6.doi:10.1016/S0009-2614(00)00588-1.
[4] LIU Y Y,DUAN Ch X,LIU H P,et al.Near-Infrared Spectrum of the A2Πi-X2Σ+(2,0) Band of CN Studied by Concentration Modulation Laser Spectroscopy[J].Journal of Molecular Spectroscopy,2001,205(1):16-19.doi:10.1006/jmsp.2000.8250.
[5] Ram R S,Davis S P,Wallace L,et al.Fourier Transform Emission Spectroscopy of the B2Σ+-X2Σ+ System of CN[J].Journal of Molecular Spectroscopy,2006,237(2):225-231.doi:10.1016/j.jms.2006.03.016.
[6] Douglas A E,Routly P M.The Spectrum of the CN Molecule[J].The Astrophysical Journal Supplement Series,1955,1:295.doi:10.1086/190010.
[7] Ito H,Ozaki Y,Suzuki K,et al.Emission Spectrum of the CN (B2Σ+-X2Σ+) Tail Band System:B2Σ+～ 4Π Perturbations in the vB=9,12,and 17 Levels[J].The Journal of Chemical Physics,1992,96(6):4195-4204.doi:10.1063/1.462838.
[8] Kulik H J,Steeves A H,Field R W.Ab Initio Investigation of High Multiplicity Σ+-Σ+ Optical Transitions in the Spectra of CN and Isoelectronic Species[J].Journal of Molecular Spectroscopy,2009,258(1-2):6-12.doi:10.1016/j.jms.2009.08.008.
[9] SHI D H,LI W T,SUN J F,et al.MRCI Study on Spectroscopic and Molecular Properties of Several Low-lying Electronic States of the CN Radical[J].Journal of Quantitative Spectroscopy & Radiative Transfer,2011,112:2335-2346.doi:10.1016/j.jqsrt.2011.06.002.
[10] Brooke J,Ram R,Western C M,et al.Einstein a Coefficients and Oscillator Strengths for the A2Π-X2Σ+(red) and B2Σ+-X2Σ+ (Violet) Systems and Rovibrational Transitions in the X2Σ+ State of CN[J].The Astrophysical Journal Supplement Series,2014,210(2):23.doi:10.1088/0067-0049/210/2/23.
[11] Agúndez M,Cernicharo J,Guélin M,et al.Astronomical Identification of CN-,the Smallest Observed Molecular Anion[J].Astronomy & Astrophysics,2010,517:L2.doi:10.1051/0004-6361/201015186.
[12] Hamzaoui S,Khleifia R,Ja?dane N,et al.Quantitative Analysis of Pathological Nails using Laser-induced Breakdown Spectroscopy (LIBS) Technique[J].Lasers in Medical Science,2011,26(1):79-83.doi:10.1007/s10103-010-0821-x.
[13] Farhadian A H,Tehrani M K,Keshavarz M H,et al.A Novel Approach for Investigation of Chemical Aging in Composite Propellants Through Laser-induced Breakdown Spectroscopy (LIBS)[J].Journal of Thermal Analysis and Calorimetry,2016,124(1):279-286.doi:10.1007/s10973-015-5116-9.
[14] LI H L,CHU W,XU H L,et al.Simultaneous Identification of Multi-combustion-intermediates of Alkanol-air Flames by Femtosecond Filament Excitation for Combustion Sensing[J].Scientific Reports,2016,6:27340.doi:10.1038/srep27340.
[15] Bose D J,Wright M W,Bogdanoff D,et al.Modeling and Experimental Assessment of CN Radiation Behind a Strong Shock Wave[J].Journal of Thermophysics and Heat Transfer,2006,20(2):220-230.doi:10.2514/1.16869.
[16] YIN Y,SHI D H,SUN J F,et al.Transition Dipole Moments and Transition Probabilities of the CN Radical[J].The Astrophysical Journal Supplement Series,2018,235(2):25.doi:10.3847/1538-4365/aab26b.
[17] Huber K P,Herzberg G.Molecular Spectra and Molecular Structure Ⅳ:Constants of Diatomic Molecules[M].Princeton:Van Nostrand Reinhold Company,1979.
[18] Duric N,Erman P,Larsson M.The Influence of Collisional Transfers and Perturbations on Measured A and B State Lifetimes in CN[J].Physica Scripta,1978,18(1):39-46.doi:10.1088/0031-8949/18/1/012.
[19] 王利东,李萍,张昌华,等.正癸烷燃烧反应中OH,CH和C2自由基的瞬态发射光谱[J].光谱学与光谱分析,2012,32(5):1166-1169.doi:10.3964/j.issn.1000-0593(2012)05-1166-04.
[20] 谈宁馨,王静波,华晓筱,等.甲基环己烷的高温燃烧机理及动力学模拟[J].高等学校化学学报,2011,32(8):1832-1837.doi:0251-0790(2011)08-1832-06.
[21] 姚倩,彭莉娟,李泽荣,等.烷烃与氢过氧自由基氢提取反应类反应能垒与速率常数的精确计算[J].物理化学学报,2017,33(4):763-768.doi:10.3866/PKU.WHXB201701091.
[22] Lewandowski H J,Hudson E R,Bochinski J R,et al.A Pulsed,Low-temperature Beam of Supersonically Cooled Free Radical OH Molecules[J].Chemical Physics Letters,2004,395(1-3):53-57.doi:10.1016/j.cplett.2004.07.050.