摘要
本文采用多组态相互作用及Davidson修正方法和全电子基组计算了SH~-阴离子的X~1∑~+,a~3∏和A~1∏态的势能曲线、电偶极矩和跃迁偶极矩.计算的光谱常数与实验值及已有的理论值符合得很好.在计算中考虑了自旋-轨道耦合效应.计算得到a~3∏_1(v'=0)?X~1∑_(0+)~+(v"=0)和A~1∏_1(v'=0)?X~1Σ_(0+)~+(v"=0)跃迁具有高对角分布的弗兰克-康登因子,分别为0.9990和0.9999;计算得到a~3∏_1和A~1∏_1态的自发辐射寿命分别为1.472和0.188 ms.A~1∏_1?X~1∑_(0+)~+跃迁存在中间态a~3∏_(0+)和a~3∏_1,但中间态对激光冷却SH~-阴离子的影响可以忽略.分别利用a~3∏_1(v'=0)? X~1∑_(0+)~+(v"=0)和A~1∏_1(v'=0)? X~1∑_(0+)~+(v"=0)跃迁构建了准闭合的能级系统,冷却所需的激光波长分别为492.27和478.57 nm.最后预测了激光冷却SH~-阴离子能达到的多普勒温度和反冲温度.这些结果为进一步实验提供了理论参数.
The potential energy curves, dipole moments, and transition dipole moments for the X~1Σ~+, a~3∏, and A~1∏electronic state of sulfur hydride anion(SH) are calculated by using the multi-reference configuration interaction method plus Davidson corrections(MRCI+Q) with all-electron basis set. The scalar relativistic corrections and core-valence correlations are also considered. In the CASSCF calculations, H(1 s) and S(3 s3 p4 s)shells are chosen as active space, and the rest orbitals S(1 s2 s2 p) as closed-shell. In the MRCI+Q calculations,the S(1 s2 s2 p) shells are used for the core-valence correlation. Spectroscopic parameters, Einstein spontaneous emission coefficient, Franck-Condon factors, and spontaneous radiative lifetimes are obtained by using Le Roy's LEVEL8.0 program. The calculated spectroscopic parameters are in good agreement with available experimental data and theoretical values. Spin-orbit coupling(SOC) effects are evaluated with Breit-Pauli operators at the MRCI+Q level. Transition dipole moments(TDMs) for the A~1∏_1?X~1∑_(0+)~+,a~3∏_(0+)?X~1∑_(0+)~+,a~3∏_1?X~1∑_(0+)~+,A~1∏_1?a~3∏_(0+) and A~1∏_1?a~3∏_1 transitions are also calculated. The strength for the A1~1∏_1?X~1∑_(0+)~+ is the strongest in these five transitions, the value of TDM at Re is-1.3636 D. We find that the value of TDM for the a~3∏~1?X~1∑_(0+)~+ transition at Re is 0.5269 D. Therefore, this transition must be taken into account to build the scheme of laser-cooled SH~-anion. Highly diagonally distributed Franck-Condon factor f_(00) for the a~3∏_1(v'=0)?X~1∑_(0+)~+(v "=0) transition is 0.9990 and the value for the A~1∏_1(v'=0)? X~1∑_(0+)~+(v" =0)transition is 0.9999. Spontaneous radiative lifetimes of τ(a~3∏_1) = 1.472 μs and τ(A~1∏_1) = 0.188 μs are obtained, which can ensure that laser cools SH~-anion rapidly. To drive the a~3∏_1?X~1∑_(0+)~+ and A~1∏_1?X~1∑_(0+)~+transitions, just one laser wavelength is required. The wavelengths are 492.27 nm and 478.57 nm for two transitions, respectively. Notably, the influences of the intervening states a~3∏_1 and a~3∏_(0+) on the A~1∏_1? X~1∑_(0+)~+ transition are small enough to implement a laser cooling project A spin-forbidden transition and a three-electronic-level transition optical scheme of laser-cooled SH~-anion are constructed, respectively. In addition, the Doppler temperatures and recoil temperatures for the a~3∏_1?X~1∑_(0+)~+ and A~1∏_1? X~1∑_(0+)~+transitions of laser-cooled SH anion are also obtained, respectively.
引文
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