Umbrella motion of the methyl cation, radical, and anion molecules - I. Potentials, energy levels and partition functionsMirco Ragni, Ana Carla P. Bitencourt, Frederico V. Prudente, Patricia R. P. Barreto and Tamara PosatiEur. Phys. J. D, 70 3 (2016) 60DOI: https://doi.org/10.1140/epjd/e2016-60530-2