氢氧化钙自由基（CaOH）的理论旋振光谱
Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)
摘要：
氢氧化钙自由基（CaOH）的旋转振动（旋转-振动-电子）光谱对系外行星大气和超冷分子的研究很有意义。本文采用高能级\textit{ab initio}理论和变分核运动计算方法，对CaOH的$\tilde{A}\,^2Π$- $\tilde{X}\,^2Σ^+$能带系统进行了理论研究。新的势能面（PES）构造的$\tilde{X}\,^2Σ^+$和$\tilde{A}\,^2Π$电子状态以及$\tilde{A}$ - $\tilde{X}$跃迁偶极矩表面（DMS）。对于$\tilde{X}\,^2Σ^+$基态，根据经验将已发表的高水平\textit{ab initio} PES精确到所有可用的实验振转能级，直到$J=15.5$，再现观测项值，均方根（rms）误差为0.06 cm $^{-1}$。使用五重zeta质量基组的大规模多参考组态相互作用（MRCI）计算被用来生成$\tilde{A}\,^2Π$状态PES和$\tilde{A}$ - $\tilde{X}$ DMS。变分计算考虑Renner-Teller和自旋轨道耦合效应，这是必不可少的正确描述的光谱的CaOH。计算的旋转振动能级的$\tilde{A}\,^2Π$状态，线列表计算到$J=125.5$，并在$ν_2$弯曲模式的CaOH的Renner-Teller分裂的分析进行了讨论。
英文摘要：
The rovibronic (rotation-vibration-electronic) spectrum of the calcium monohydroxide radical (CaOH) is of interest to studies of exoplanet atmospheres and ultracold molecules. Here, we theoretically investigate the $\tilde{A}\,^2Π$--$\tilde{X}\,^2Σ^+$ band system of CaOH using high-level \textit{ab initio} theory and variational nuclear motion calculations. New potential energy surfaces (PESs) are constructed for the $\tilde{X}\,^2Σ^+$ and $\tilde{A}\,^2Π$ electronic states along with $\tilde{A}$--$\tilde{X}$ transition dipole moment surfaces (DMSs). For the ground $\tilde{X}\,^2Σ^+$ state, a published high-level \textit{ab initio} PES is empirically refined to all available experimental rovibrational energy levels up to $J=15.5$, reproducing the observed term values with a root-mean-square (rms) error of 0.06~cm$^{-1}$. Large-scale multireference configuration interaction (MRCI) calculations using quintuple-zeta quality basis sets are employed to generate the $\tilde{A}\,^2Π$ state PESs and $\tilde{A}$--$\tilde{X}$ DMSs. Variational calculations consider both Renner-Teller and spin-orbit coupling effects, which are essential for a correct description of the spectrum of CaOH. Computed rovibronic energy levels of the $\tilde{A}\,^2Π$ state, line list calculations up to $J=125.5$, and an analysis of Renner-Teller splittings in the $ν_2$ bending mode of CaOH are discussed.
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