ExoMol molecular line lists - XIII: The spectrum of CaO

TL;DR

This paper presents a comprehensive and refined spectroscopic line list for calcium oxide (CaO), covering all bound ro-vibronic transitions across five electronic states, useful for high-temperature astrophysical applications.

Contribution

It provides the first fully coupled theoretical model for CaO, extending and refining previous experimental data, and offers the most complete spectroscopic transition catalogue for this molecule.

Findings

Extended the energy levels to J=79-118

Reassigned many experimental vibronic states

Produced a comprehensive line list for temperatures up to 5000 K

Abstract

An accurate line list for calcium oxide is presented covering transitions between all bound ro-vibronic levels from the five lowest electronic states \X, \Ap, \A, \astate, and \bstate. The ro-vibronic energies and corresponding wavefunctionts were obtained by solving the fully coupled Schr\"{o}dinger equation. \textit{Ab initio} potential energy, spin-orbit, and electronic angular momentum curves were refined by fitting to the experimental frequencies and experimentally derived energies available in the literature. Using our refined model we could (i) reassign the vibronic states for a large portion of the experimentally derived energies [van Groenendael A., Tudorie M., Focsa C., Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255], (ii) extended this list of energies to $J=79-118$ and (iii) suggest a new description of the resonances from the \A--\X\ system. We used high level \textit{ab initio} electric dipole moments reported previously [Khalil H., Brites V., Le Quere F., Leonard C., 2011, Chem. Phys., 386, 50] to compute the Einstein A coefficients. Our work is the first fully coupled description of this system. Our line list is the most complete catalogue of spectroscopic transitions available for $^{40}$Ca$^{16}$O and is applicable for temperatures up to at least 5000~K. CaO has yet to be observed astronomically but its transitions are characterised by being particularly strong which should facilitate its detection. The CaO line list is made available in an electronic form as supplementary data to this article and at \url{www.exomol.com}.