低激发态CN自由基光谱参数的理论研究

Theoretical Study on Spectroscopic Properties of the Low Excited States for CN Radical

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(Te,Re,ωe,ωeχe,Be,αe),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 f00 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.