Microwave rest frequencies were obtained from laboratory measurements and from observations of TMC-1 by
(1) J. Cernicharo, C. Cabezas, Y. Endo, M. Agúndez, B. Tercero, J. R. Pardo, N. Marcelino, and P. de Vicente, 2021, Astron. Astrophys. 650, Art. No. L14.
Additional higher order parameters were estimated from the isoelectronic HC₂CHS, see e070511.cat.
The calculations are sufficiently accurate for observations of cold and possibly even luke-warm sources. Transition frequencies were trancated in frequency, in J to 32, in K_a to 6 and 3 for a- and b-type transitions, respectively. Transition frequencies with J > 15 or b-type transitions with K_a ≥ 2 should be viewed with great caution.
The ¹⁴N hyperfine splitting is resolvable at lower frequencies or at lower quantum numbers. Therefore, a separate calculation with hyperfine structure is available with J up to 15.
The dipole moment is from a quantum-chemical calculation in (1).