Extensive experimental laboratory frequencies up to 26 GHz, with resolved hyperfine structure (HFS) splitting and frequencies without HFS splitting from astronomical observations between 31 and 50 GHz were reported in
(1) C. Cabezas, M. Agúndez, Y. Endo, B. Tercero, Y.-P. Lee, N. Marcelino, P. de Vicente, and J. Cernicharo, 2024, Astron. Astrophys. 686, Art. No. L3.
The present calculation includes estimates of d₂ and D_K. The calculation was truncated in J, K_a, and frequency. The calculations should be sufficient for observations in cold and possibly luke-warm sources. Some caution is advised for a-type transitions with K_a > 2 and for b-type transitions with K_a = 2. The ¹⁴N hyperfine splitting may be resolvable at lower frequencies or at lower quantum numbers. Therefore, a separate calculation with hyperfine structure is available that is essentially equivalent to the entry without HFS splitting. The spin-multiplicity of the ¹⁴N nucleus was considered in the calculation of the partition function.
The dipole moment components are from a quantum-chemical calculation in (1).