基于ab initio的BD+离子激光冷却理论研究

摘要

基于相关一致基组aug-cc-pV5Z,采用内收缩多参考组态相互作用方法计算了BD+离子两个最低解离极限B+(1Sg)+D(2Sg)和B+(3Pu)+D(2Sg)对应的5个Λ—S态(X2Σ+,A2Π,B2Σ+,a4Π和b4Σ+)的势能曲线和跃迁偶极矩.根据计算结果,求解核运动的径向薛定谔方程得到相应电子态的振-转光谱常数、Franck-Condon(F-C)因子和振动能级辐射寿命.其中A2Π—X2Σ+的F-C因子(f00=0.923)、辐射寿命(τ=235 ns)满足激光直接冷却的条件.因此,我们基于分子转动跃迁提出了一个可实现Doppler激光冷却的光循环方案:A2Π1/2(υ′=0)—X2Σ+(υ"=0,1),其中υ′=0中包含2个转动能级,υ"=0和υ"=1中分别包含6个和4个转动能级.根据方案,模拟了激光冷却过程中的分子布居数动力学变化过程,并计算了初速度为100 m/s的BD+,历经5.4 ms散射1150个光子可减速到4.6 m/s、温度为13 mK.%Based on consistent basis set aug-cc-pV5Z, five low-lying potential energy curves and transition dipole moments X2Σ+, A2Π, B2Σ+, a4Π and b4Σ+ of BD+ are calculated by using internally contracted multi-reference configuration interaction approach. According to the calculation results, ro-vibrational levels of theses electronic states are derived through solving the radial Schr?dinger equation ro-vibrational equation, and then the molecular parameters, Franck-Condon factors (FCFs) and radiation life are obtained by fitting and calculations. The FCFs (f00=0.923) and radiation life for υ′′ =0 (τ =235 ns) of A2Π–X2Σ+ are suitable for achieving rapid laser cooling. Therefore, an optical-cycle for Doppler laser cooling scheme is proposed: the system includes the A2Π1/2(υ′ = 0)–X2Σ+(υ′′ = 0, 1), where the case of υ′ = 0 contains 2 rotational levels, the cases of υ′′ = 0 and υ′′ = 1 contain 6 and 4 rotational levels, respectively. According to the proposal, we simulate the dynamic process of the molecular population in laser cooling. The BD+ can be decelerated from initial velocity of 100 m/s to 4.6 m/s (13 mK) after scattering 1150 photons during 5.4 ms.