ExoMol Line Lists -- LXII: Ro-Vibrational Energy Levels and Line-Strengths for the Propadienediylidene (C3) in its Ground Electronic State

Abstract

Improved opacities are needed for modelling the atmospheres and evolution of cool carbon-rich stars and extra-solar planets; in particular, contributions made by the astrophysically important propadienediylidene (C${}_3$) molecule need, at a minimum, to be determined using a line list which includes all significant transitions in the energy range of interest. We report variational calculations giving ro-vibrational energy levels and corresponding line-strengths for ${}^{12}$C${}_3$, ${}^{12}$C${}^{13}$C${}^{12}$C and ${}^{12}$C${}^{12}$C${}^{13}$C. In the ${}^{12}$C${}_3$ case we obtain 2166503 ro-vibrational state energies $\le$ 20000 cm${}^{-1}$ for the electronic ${\tilde{X}}^1{\Sigma }_g^{+}$ ground-state. Comparison with experiment indicates a maximum error of +/- 0.03 cm${}^{-1}$ in calculated positions of lines involving an upper state energy $\lesssim$ 4000 cm${}^{-1}$. For lines with upper state energies $\gtrsim$ 4000 cm${}^{-1}$ to have comparable line-position accuracies, conical intersections would need to be accounted for in an adopted potential energy surface. Line lists and associated opacities are provided in the ExoMol Database http://www.exomol.com ).

To be published in Monthly Notices of the Royal Astronomical Society