The observed transitions were taken from
(1) L. Bizzocchi, M. Melosso, L. Dore, C. Degli Esposti, F. Tamassia, D. Prudenzano, V. Lattanzi, J. Laas, S. Spezzano, B. M. Giuliano, C. P. Endres, and P. Caselli, 2018, Astrophys. J. 863, Art. No. 3; additional far-infrared data were taken from
(2) S. Bailleux, M. A. Martin-Drumel, L. Margulès, O. Pirali, G. Wlodarczak, P. Roy, E. Roueff, M. Gerin, A. Faure, and P. Hily-Blant, 2012, Astron. Astrophys. 538, Art. No. A135.
The N = 1 – 0 transition may be the only one with chances of being observable. The 2 – 1 transition is quite well constrained also. Predictions to higher values of N should be viewed with caution.
The dipole moment was taken from the main isotopic species published in
(3) E. A. Scarl and F. W. Dalby, 1974, Can. J. Phys. 52, 1429.