In this work, the $({\mathrm{A}}^2{\mathrm{\Sigma }}^{+}-{\mathrm{X}}^2\mathrm{\Pi })$ band system of LiS is theoretically studied employing novel and accurate functional forms. For such, ab initio electronic energies are firstly calculated using an internally contracted multireference configuration interaction with Davidson modification (MRCI + Q) associated with aug-cc-pV(5 + d) Z basis set. These energies are subsequently fitted to the extended Hartree-Fock approximate correlation energy (EHFACE) model. Based on the obtained functions, molecular properties as spectroscopic parameters, rovibrational levels, and classical turning points were derived. For the first time, accurate Franck-Condon factors (FCF), r-centroids, and Einstein coefficients for spontaneous emission are reported. Calculated radiative lifetimes for the excited state ${\mathrm{A}}^2{\mathrm{\Sigma }}^{+}$ are of the order of milliseconds. The recoil temperature (${\mathrm{T}}_{\mathrm{recoil}}$) is also calculated, indicating an ultracold temperature for this molecule. Besides, the results shown in this study can be considered as reliable guidelines for experimental measurements.

在这项工作中， $（{\mathrm{一种}}^2{\mathrm{\Sigma }}^{+}--{\mathrm{X}}^2\mathrm{\Pi }）$从理论上研究了LiS的带系统，采用了新颖而准确的功能形式。为此，首先使用具有与aug-cc-pV（5 + d）Z基组相关联的Davidson修改（MRCI + Q）的内部收缩多参考配置相互作用来计算从头算起的电子能量。随后将这些能量拟合到扩展的Har​​tree-Fock近似相关能量（EHFACE）模型。基于获得的函数，得出分子性质作为光谱参数，振动水平和经典转折点。首次报道了精确的弗兰克-康登因子（FCF），r重心和自发发射的爱因斯坦系数。计算激发态的辐射寿命${\mathrm{一种}}^2{\mathrm{\Sigma }}^{+}$大约是毫秒。后坐温度${\mathrm{Ť}}_{\mathrm{畏缩}}$）也被计算出来，表明该分子的超冷温度。此外，这项研究中显示的结果可以被认为是进行实验测量的可靠指南。