KCs 的 $a^3Σ^+$ 态再探：超精细结构分析与势能曲线精化
The $a^3Σ^+$ state of KCs revisited: hyperfine structure analysis and potential refinement
AI总结：
通过高分辨率光谱和从头算分析，系统研究了KCs分子a^3Σ^+态的超精细结构，并精化了势能曲线，解离能精确至267.21(1) cm⁻¹。
摘要：
利用傅里叶变换光谱仪 IFS125-HR (Bruker) 在最高可达的 0.0063 cm${}^{-1}$ 光谱分辨率下，记录了从 $^{39}$K$^{133}$Cs 分子的基态 $X^1Σ^+$ 激发至 $c^3Σ^+(v_{c},J_{c}=N_{c})\rightarrow a^3Σ^+(v_{a},N_{a} = J_{c} \pm 1)$ 跃迁的激光诱导荧光光谱。对 $a^3Σ^+$ 态在 $v_{a} \in [0, 27]$ 和 $N_{a} \in [24, 90]$ 范围内能级的超精细结构（HFS）的系统研究表明，分裂随 $v_{a}$ 单调增加。光谱研究得到了 $X^1Σ^+$ 和 $a^3Σ^+$ 态中磁超精细相互作用的从头算计算的支持。发现的电子矩阵元随核间距 $R$ 的变化与观测到的 HFS 的 $v_{a}$ 依赖性吻合良好。利用现有的关于 $a^3Σ^+$ 态的整套实验数据改进了势能曲线，特别是在底部附近，提供了精化的解离能 $D_e$=267.21(1) cm${}^{-1}$。从头算 HFS 矩阵元与经验 $X^1Σ^+$ 和 $a^3Σ^+$ 势能曲线在发明的耦合通道退微扰模型框架内相结合，在直至共同解离极限的范围内，以 0.003 cm${}^{-1}$ 的精度再现了两个基态的实验项值。
英文摘要：
Laser-induced fluorescence spectra of the $c^3Σ^+(v_{c},J_{c}=N_{c})\rightarrow a^3Σ^+(v_{a},N_{a} = J_{c} \pm 1)$ transitions excited from the ground $X^1Σ^+$ state of $^{39}$K$^{133}$Cs molecule were recorded with Fourier-transform spectrometer IFS125-HR (Bruker) at the highest achievable spectral resolution of 0.0063 cm${}^{-1}$. Systematic study of the hyperfine structure (HFS) of the $a^3Σ^+$ state for levels with $v_{a} \in [0, 27]$ and $N_{a} \in [24, 90]$ shows that the splitting monotonically increases with $v_{a}$. The spectroscopic study was supported by ab initio calculations of the magnetic hyperfine interaction in $X^1Σ^+$ and $a^3Σ^+$ states. The discovered variation of the electronic matrix elements with the internuclear distance $R$ is in a good agreement with the observed $v_{a}$-dependencies of the HFS. Overall set of available experimental data on the $a^3Σ^+$ state was used to improve the potential energy curve particularly near a bottom, providing the refined dissociation energy $D_e$=267.21(1) cm${}^{-1}$. The ab initio HFS matrix elements, combined with the empirical $X^1Σ^+$ and $a^3Σ^+$ PECs in the framework of the invented coupled-channel deperturbation model, reproduce the experimental term values of both ground states within 0.003 cm${}^{-1}$ accuracy up to their common dissociation limit.
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