ExoMol line lists - LXII. Ro-vibrational energy levels and line strengths for the propadienediylidene (C3) in its ground electronic state

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 C-12(3), (CC12)-C-12-C-13 C, and (CCC)-C-12-C-12-C-13. In the C-12(3) case, we obtain 2166 503 ro-vibrational state energies <= 2000 cm(-1) for the electronic (X) over tilde (1) E-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 (sic) 4000 cm(-1). For lines with upper state energies (sic)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 data base (http://www.exomol.com).