LiCl^(-)阴离子的光谱性质和跃迁性质

Spectroscopic and transition properties of LiCl-anion

采用多参考组态相互作用方法结合全电子基组计算了LiCl^(-)阴离子5个电子态(X^(2)Σ^(+),A^(2)∏,B^(2)Σ^(+),3^(2)Σ+,2^(2)∏)的电子结构.为了得到精确的光谱常数,计算中考虑了Davidson修正、芯-价电子关联效应和自旋-轨道耦合效应.拟合得到各电子态的光谱常数、分子常数、自发辐射速率和自发辐射寿命.基态的光谱常数与实验值和其他理论值符合较好,同时报道了LiCl^(-)阴离子激发态的光谱常数以及其到基态的跃迁性质.计算结果表明A^(2)∏↔X^(2)Σ+跃迁具有高对角分布的弗兰克-康登因子f00,第一激发态A^(2)∏有较短的自发辐射寿命.构造A^(2)∏(ν′)↔X^(2)Σ+(ν′′)准循环跃迁进行激光冷却LiCl^(-)阴离子需要一束主激光和两束抽运激光.以上结果预测了激光冷却LiCl^(-)阴离子是可行的.

The electronic structure of the X^(2)Σ^(+),A^(2)∏,B^(2)Σ^(+),3^(2)Σ+,and 2^(2)∏state of LiCl^(-)anion are performed at an MRCI+Q level.Davison correction,core-valence correction and spin-orbit coupling effect are also considered.The ground state X^(2)Σ+of LiCl^(-)anion correlates with the lowest dissociation channel Li(2Sg)+Cl^(-)(1Sg);the A^(2)∏state and B2Σ+state correlate with the second dissociation channel Li(2Pu)+Cl^(-)(1Sg);the 32Σ+state and 22Πstate correlate with the third dissociation channel Li–(1Sg)+Cl^(-)(2Pu).Spectroscopic parameters are calculated by solving the radial Schröedinger equation.The equilibrium internuclear distance Re of the ground state X^(2)Σ+is 2.1352Å,which is a little bigger than the experimental datum,with an error being 0.5%.It is a deep potential well,and the dissociation energy De is 1.886 eV.These values are in good agreement with experimental data.The A^(2)∏state is at 13431.93 cm^(-1) above the X^(2)Σ+state.The Re is 2.1198Å,which is only 0.0154Åsmaller than that of the X^(2)Σ+state.The values of energy level Gνand rotational constant Bνof fiveΛ-S states are also calculated.The values are in good agreement with available theoretical ones.The electronic structures of the excited states are also reported.The SOC effect weakly influences the spectroscopic parameters for the X^(2)Σ+1/2,A^(2)Π1/2,A^(2)Π3/2,and B2Σ+1/2 state.From the analysis of the SO matrix,it can be seen that the SOC effect plays a little role in realizing the A^(2)Π↔X^(2)Σ+transition,so,it can be ignored.The scheme of laser cooling of LiCl^(-)anion has constructed at a spin–free level.The A^(2)∏(ν′)↔X^(2)Σ+(v′′)transition has a highly diagonally distributed Franck-Condon factor f00=0.9898,the calculated branching ratio of the diagonal term R00 is 0.9893,and spontaneous radiative lifetime of A^(2)∏is 35.45 ns.A main pump laser and two repumping lasers for driving the A^(2)∏(ν′)↔X^(2)Σ+(v′′)transitions are required.The laser wavelengths are 744.10,774.30 and 772.42 nm,respectively.Owing to the summation of R00,R01,and R02 being closer to 1,the A^(2)∏(ν′)↔X^(2)Σ+(v′′)transition is a quasicycling transition.These results imply that the LiCl^(-)anion is a candidate for laser cooling.