碱土金属卤化物MX的电子结构和光谱跃迁特性的研究

Alkaline-earth monohalides MX is composed of a strong dipole system with positive ions of the doubly closed shell nuclei M2+X-, which has nine valence electrons outside the molecular closed shell and with larger state density. The coupling interactions between excited states could affect the electronic structures and dissociation dynamics, especially for alkaline-earth monohalides with larger atomic number, spin-orbit coupling effect can lead to predissociation of some electronic states, which causes to the difficulties in analysis of spectra and lack of information on the spectroscopy of these molecules and ions. Hence, there is an urgent need of theoretical work that provides the information on the electronic structures and spectroscopic properties of excited states of these molecules..This project adopts the multireference configuration interaction within contracted method, combining with the non-shrinkageand full electron basis to study the electronic structure and spectral transition property of the ground state and the low excited state of MX molecules, introducing the Davidson modification, core valence correlation and relativistic effect correction in calculations. Then obtain the accurate electronic structures, spectroscopic parameters and the radiation lifetimes of low-lying excited states. Finally, illuminate the influence of the coupling of the excited states on the process of the predissociation and spectra of excited states. This will help to understand to the electronic structures, spectral transition properties and dissociation dynamics. It is expected that these results should be very useful for guiding further experimental measurements and identify on relative systems.

碱土金属卤化物MX是由强烈的偶极系统组成的带正电荷的离子双闭合壳层核M2+X-，其闭壳层外有九个价电子，电子态密度非常大。激发态间的耦合效应对电子结构和解离动力学过程有显著的影响，特别对具有较大原子序数的碱土金属卤化物，自旋-轨道耦合作用会使一些电子态出现预解离现象，增加了这类分子及离子光谱分析的难度，导致获得这类分子的光谱信息较少，因此需要理论计算来获得分子激发态的电子结构和光谱跃迁性质的相关信息。.本项目拟采用内收缩多参考组态相互作用方法，结合完全非收缩的全电子基研究MX分子基态和低激发态的电子结构和光谱跃迁性质，计算中引入Davidson修正、核价相关和相对论效应修正，获得高精度的电子结构、光谱参数和激发态较低的振动能级的辐射寿命，阐明激发态之间的耦合作用对预解离过程和激发态光谱的影响。这有助于加深对激发态的电子结构、跃迁性质和解离动力学过程的认识，为相关体系的光谱实验提供理论支持。

碱土金属卤化物由于电子密度较大，内壳层电子会直接影响电子结构和光谱性质的计算，再加上激发态间耦合、旋轨-耦合、电子相关和相对论效应都会显著地影响它们的电子结构和光谱性质，致使光谱实验测量工作具有较大难度。如何较好地修正各种效应来提高理论计算精度，从而为实验研究提供必要的参考是目前该类分子研究的重点和难点。通过本项目的支持，课题组采用量子计算软件程序包Molpro2012，利用Davidson修正的内收缩多参考组态相互作用(MRCI+Q)方法，结合相关一致全电子基aug-cc-pwCV5Z和有效芯势(ECP28)aug-cc-pV5Z-PP优化计算了MgH、MgBr、MgCl、MgI、SrCl、SrBr和SrI分子低激发电子态的势能曲线、光谱参量和跃迁特性。研究结果表明，当计算中同时引入核价电子相关、自旋-轨道耦合效应和相对论标量效应修正分子的势能函数，从而使获得的光谱参量与已有的实验结果吻合更好。在此基础上，课题组成员编制和修改了 LEVEL8.0程序软件，拟合得到了分子的振动能级、能级差和Franck-Condon (FC) 因子，结合优化计算得到的跃迁偶极矩，精确计算得出该类分子体系的爱因斯坦系数和辐射寿命，结果也与已有的实验结果吻合较好。这为碱土金属卤化物分子激发态的光谱实验提供理论参考，同时为构建该类分子激光冷却方案和进行激光冷却实验提供参考。