Zhang Qing-Qing, Yang Chuan-Lu, Wang Mei-Shan, Ma Xiao-Guang, Liu Wen-Wang
School of Physics and Optoelectronics Engineering, Ludong University, Yantai 264025, People's Republic of China.
School of Physics and Optoelectronics Engineering, Ludong University, Yantai 264025, People's Republic of China.
Spectrochim Acta A Mol Biomol Spectrosc. 2017 Oct 5;185:365-370. doi: 10.1016/j.saa.2017.06.001. Epub 2017 Jun 3.
The potential energy curves and transition dipole moments of 1Σ, 2Σ, 1Π and 2Π states of NH cation and NH anion are calculated by using multi-reference configuration interaction method and large all-electron basis sets. Based on the obtained potential energy curves, the rotational and vibrational energy levels of the states are obtained by solving the Schrödinger equation of nuclear movement. The calculated spectroscopic parameters for NH cation and NH anion are in good agreement with available theoretical and experimental results. The spin orbit coupling effect of the Π states for both NH cation and NH anion are calculated. The feasibility of laser cooling of the two molecules is examined by using the results of the molecular structure and spectroscopy. The highly diagonal Franck-Condon factors for the 1Π (v″=0)↔1Σ (v'=0) transition of NH and NH are 0.821 and 0.999, while the radiative lifetimes of the 1Σ (v'=0) state for the two molecules are 384ns and 52.4ns, respectively. The results indicate that NH cation and NH anion are good candidate molecules for laser cooling. The cooling scheme via Sisyphus process for the NH cation and NH anion are proposed in the paper. The laser wavelengths for the close cycles of the absorption and radiation are also determined. Unfortunately, the potential energy curve of the ground state of the neutral NH molecule shows that the auto-detachment of NH anion is possible, implying the optical scheme of laser cooling for NH anion is not easy to achieve in the experiment although it has larger Franck-Condon factor.
采用多参考组态相互作用方法和大的全电子基组计算了NH阳离子和NH阴离子的1Σ、2Σ、1Π和2Π态的势能曲线和跃迁偶极矩。基于所得到的势能曲线，通过求解核运动的薛定谔方程得到了这些态的转动和振动能级。计算得到的NH阳离子和NH阴离子的光谱参数与现有的理论和实验结果吻合良好。计算了NH阳离子和NH阴离子的Π态的自旋轨道耦合效应。利用分子结构和光谱的结果研究了这两种分子激光冷却的可行性。NH和NH的1Π(v″=0)↔1Σ(v'=0)跃迁的高对角弗兰克-康登因子分别为0.821和0.999，而这两种分子的1Σ(v'=0)态的辐射寿命分别为384ns和52.4ns。结果表明，NH阳离子和NH阴离子是激光冷却的良好候选分子。本文提出了通过西西弗斯过程对NH阳离子和NH阴离子进行冷却的方案。还确定了吸收和辐射近循环的激光波长。遗憾的是，中性NH分子基态的势能曲线表明NH阴离子可能会自动解离，这意味着尽管NH阴离子具有较大的弗兰克-康登因子，但在实验中实现其激光冷却的光学方案并不容易。
