Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)

• Published in: The Journal of chemical physics Vol. 154; no. 23
• Main Authors: Owens, Alec, Clark, Victoria H. J., Mitrushchenkov, Alexander, Yurchenko, Sergei N., Tennyson, Jonathan
• Format: Journal Article
• Language: English
• Published: 21.06.2021
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/5.0052958

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 Ã2Π–X̃2Σ+ band system of CaOH using high-level ab initio theory and variational nuclear motion calculations. New potential energy surfaces (PESs) are constructed for the X̃2Σ+ and Ã2Π electronic states along with ÖX̃ transition dipole moment surfaces (DMSs). For the ground X̃2Σ+ state, a published high-level 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 error of 0.06 cm−1. Large-scale multireference configuration interaction calculations using quintuple-zeta quality basis sets are employed to generate the Ã2Π state PESs and ÖX̃ 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 Ã2Π state, line list calculations up to J = 125.5, and an analysis of Renner–Teller splittings in the ν2 bending mode of CaOH are discussed.