Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)

Abstract

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 $\tilde{A}{}^2\Pi$--$\tilde{X}{}^2{\Sigma }^{+}$ 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 $\tilde{X}{}^2{\Sigma }^{+}$ and $\tilde{A}{}^2\Pi$ electronic states along with $\tilde{A}$--$\tilde{X}$ transition dipole moment surfaces (DMSs). For the ground $\tilde{X}{}^2{\Sigma }^{+}$ 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 $\tilde{A}{}^2\Pi$ 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 $\tilde{A}{}^2\Pi$ state, line list calculations up to $J=125.5$, and an analysis of Renner-Teller splittings in the ${\nu }_2$ bending mode of CaOH are discussed.

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Cited by in corpus (2)

• ExoMol line lists -- XLVII. Rovibronic molecular line list of the calcium monohydroxide radical (CaOH)
• Low-$J$ transitions in ${\tilde{A}}^2\Pi (0,0,0)-{\tilde{X}}^2{\Sigma }^{+}(0,0,0)$ band of buffer-gas-cooled CaOH