物理学报2024，Vol.73Issue(2)：101-108,8.DOI:10.7498/aps.73.20230742
CaSH分子高精度电子结构计算及用于激光制冷目标分子的理论分析
High-precision electron structure calculation of CaSH molecules and theoretical analysis of its application to laser-cooled target molecules
摘要
Abstract
The CaSH molecule is an important target in the field of laser cooling non-linear polyatomic molecules.Successful cooling of such molecules marks a breakthrough of the technical limitations of laser cooling diatomic and linear triatomic molecules.To identify the possible optical cycle in cooling CaSH,precise geometries of the CaSH ground state and the three lowest excited states,along with their excitation energy,are determined by utilizing the EA-EOM-CCSD(electron attachment equation-of-motion coupled cluster singles and doubles)method,in combination with energy extrapolation using cc-pVXZ/cc-pCVXZ(X = T,Q)serial basis sets.Geometric parameters of the ground state(X)2A′are found to be RCaS= 2.564 Å,RSH= 1.357 Å,and∠CaSH= 91.0°.Additionally,the equilibrium geometries of three excited states are also obtained.The(B)2A″ state has a similar equilibrium structure to the ground state,while the Ã2A′ and(C)2A′ states exhibit significant conformer distortions.Specifically,the CaS bond of the Ã2A′ state and(C)2A′ state tend to contract,and the CaSH angel bends by 5° relative to the ground state.The vertical excitation energy from the ground state to Ã2A′,(B)2A″ and(C)2A′ are of 1.898,1.945 and 1.966 eV,respectively,which are in good agreement with the previous experimental results.Moreover,the potential energy surfaces of the four lowest electronic states of CaSH are calculated by EA-EOM-CCSD with 3ζ level of basis sets.The nuclear equations of motion are solved to obtain the vibrational frequencies of the CaS bond stretching and CaSH bending.The vibrational frequencies of the(0,1,0)mode and the CaS stretching frequency of four states are 316 cm-1,315 cm-1,331 cm-1 and 325 cm-1,which are in close agreement with the available experimental results.The frequencies of the CaSH bending mode are presented for the first time,with the values of 357 cm-1,396 cm-1,384 cm-1,411 cm-1 for the(X)2A′,Ã2A′,(B)2A″ and(C)2A′ states,respectively.Theoretical calculations give the Frank-Condon factors of 0.9268,0.9958 and 0.9248 for the(X)2A′(0,0,0)to Ã2A′(0,0,0),(B)2A″(0,0,0)and(C)2A′(0,0,0)transitions.All three excited states are the bright states with considerable oscillator strength relative to the ground state.Based on the Frank-Condon factor and lifetime of excited states,the(X)2A′(0,0,0)→(B)2A″(0,0,0)transition is regarded as the main cooling cycle for the CaSH molecule.The corresponding pump light wavelength is 678 nm.By exciting the vibrational excited states(0,1,0)and(0,0,1)of the(X)2A′ state to Ã2A′(0,0,0)using lasers at 666 nm and 668 nm,respectively,the optical cooling branch ratio of CaSH is expected to exceed 0.9998.关键词
激光冷却/激发态/Franck-Condon因子/光学循环Key words
laser cooling/excited state/Franck-Condon factor/optical cycle引用本文复制引用
冯卓,索兵兵,韩慧仙,李安阳..CaSH分子高精度电子结构计算及用于激光制冷目标分子的理论分析[J].物理学报,2024,73(2):101-108,8.基金项目
国家自然科学基金(批准号:21873077)和陕西省自然科学基础研究计划(批准号:2021JM-311)资助的课题. Project supported by the National Natural Science Foundation of China(Grant No.21873077)and the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2021JM-311). （批准号:21873077）
