Gao Yu-feng, Gao Tao
Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China.
Phys Chem Chem Phys. 2015 Apr 28;17(16):10830-7. doi: 10.1039/c5cp00025d.
The feasibility of laser cooling BH and GaF is investigated using ab initio quantum chemistry. The ground state X (1)Σ(+) and first two excited states (3)Π and (1)Π of BH and GaF are calculated using the multireference configuration interaction (MRCI) level of theory. For GaF, the spin-orbit coupling effect is also taken into account in the electronic structure calculations at the MRCI level. Calculated spectroscopic constants for BH and GaF show good agreement with available theoretical and experimental results. The highly diagonal Franck-Condon factors (BH: f00 = 0.9992, f11 = 0.9908, f22 = 0.9235; GaF: f00 = 0.997, f11 = 0.989, f22 = 0.958) for the (1)Π (v' = 0-2) → X (1)Σ(+) (v = 0-2) transitions in BH and GaF are determined, which are found to be in good agreement with the theoretical and experimental data. Radiative lifetime calculations of the (1)Π (v' = 0-2) state (BH: 131, 151, and 187 ns; GaF: 2.26, 2.36, and 2.48 ns) are found to be short enough for rapid laser cooling. The proposed laser cooling schemes that drive the (1)Π (v' = 0) → X (1)Σ(+) (v = 0) transition use just one laser wavelength λ00 (BH: 436 nm, GaF: 209 nm). Though the cooling wavelength of GaF is deep in the UVC, a frequency quadrupled Ti:sapphire laser (189-235 nm) could be capable of generating useful quantities of light at this wavelength. The present results indicate that BH and GaF are two good choices of molecules for laser cooling.
利用从头算量子化学方法研究了激光冷却BH和GaF的可行性。使用多参考组态相互作用（MRCI）理论水平计算了BH和GaF的基态X (1)Σ(+)以及前两个激发态(3)Π和(1)Π。对于GaF，在MRCI水平的电子结构计算中还考虑了自旋轨道耦合效应。计算得到的BH和GaF的光谱常数与现有的理论和实验结果吻合良好。确定了BH和GaF中(1)Π (v' = 0 - 2) → X (1)Σ(+) (v = 0 - 2)跃迁的高度对角化的弗兰克 - 康登因子（BH：f00 = 0.9992，f11 = 0.9908，f22 = 0.9235；GaF：f00 = 0.997，f11 = 0.989，f22 = 0.958），发现其与理论和实验数据吻合良好。(1)Π (v' = 0 - 2)态的辐射寿命计算结果（BH：131、151和187 ns；GaF：2.26、2.36和2.48 ns）表明其足够短，可用于快速激光冷却。所提出的驱动(1)Π (v' = 0) → X (1)Σ(+) (v = 0)跃迁的激光冷却方案仅使用一个激光波长λ00（BH：436 nm，GaF：209 nm）。尽管GaF的冷却波长处于深紫外区，但四倍频钛宝石激光器（189 - 235 nm）能够产生该波长下的有用光量。目前的结果表明，BH和GaF是激光冷却分子的两个良好选择。
