一溴化锶分子低激发态的光谱特性研究

Spectral characteristics of low excited state of strontium monobromide molecule

采用内收缩多参考组态相互作用(ic-MRCI)方法和相对论有效芯赝势基(aug-cc-pV5Z-PP),优化计算一溴化锶(^(88)Sr^(79)Br)分子14个低激发电子态的电子结构和单点能.为了获得更加精确的光谱参数,引入Davidson、核价电子相关和相对论效应修正单点能,根据优化修正得到的单点能分析获得了最低5个束缚态的势能曲线和偶极矩.利用LEVEL8.0程序拟合修正的势能曲线,得到各束缚态的光谱常数、分子常数和振动能级等光谱性质参数.对比发现本文计算的结果与实验值吻合较好,最后给出了跃迁性质参数Franck-Condon因子和辐射寿命.这些光谱特性参数为进一步实验测量和构建分子激光冷却方案提供理论支持.

The electronic structures and single point energy of 14 lowest electronic states of ^(88)Sr^(79)Br molecule are optimized by using the internal contraction multi-reference configuration interaction method and relativistic effective core pseudo-potential basis. Because ^(88)Sr^(79)Br molecule belongs to heavy element system, the single point energy must be corrected to obtain more accurate spectral parameters. Therefore, Davidson is introduced to correct the energy inconsistency, nuclear valence correlation is used to correct the electron correlation effect of inner shell and valence shell, and the relativistic scalar effect is corrected by calculating the third-order Douglas-Kroll-Hess Hamilton single electron integral. According to the single point energy calculated by the modified optimization, the potential energy curves, electric dipole moments, and transition dipole moments of 14 lowest electronic states are obtained. Using the latest LEVEL8.0 program to fit the modified potential energy curve, the spectral constants, molecular constants and vibration energy levels of 5 lowest bound states of^(88)Sr^(79)Br molecule are given. In order to explain the changing trend of spectral constants of homologous compounds, the spectral parameters of each compound are compared and analyzed in this paper. At the same time, the vibration energy levels and molecular constants of^(88)Sr^(79)Br molecule are also fitted and calculated for analyzing the influence of isotopes. The comparative analysis shows that the results of^(88)Sr^(79)Br molecule are in better agreement with the experimental values. Finally, the Franck-Condon factors are gained by fitting the optimized single point energy and transition dipole moment of^(88)Sr^(79)Br molecule. The transition band with the largest factor and obvious diagonalization is selected by analyzing the Franck-Condon factor of each transition band,and whether it meets the conditions for selecting laser cooling molecular system is judged. The radiation lifetimes of the transitions from the lowest two excited states to the ground state are calculated by combining the transition dipole moment, Franck-Condon factor, single point energy and vibration energy level of each electronic state. The results of this paper are in good agreement with the experimental values, which shows that the method in this paper is reliable. These spectral characteristic parameters provide theoretical support for further experimental measurement and construction of molecular laser cooling scheme of^(88)Sr^(79)Br molecule.