The millimeter spectrum was reported in
(1) A. Guarnieri, R. Hinze, M. Krüger, H. Zerbe-Foese, D. Lentz, and D. Preugschat, 1992, J. Mol. Spectrosc. 156, 39.
The ground state fundamental rotational transition with ¹⁴N hyperfine splitting was published in
(2) M. Krüger, W. Stahl, and H. Dreizler, 1993, J. Mol. Spectrosc. 158, 298.
The ¹⁴N nuclear spin-rotation parameter was kept fixed to the value from a quantum-chemical calculation by
(3) H. S. P. Müller, 2020, unpublished.
One line of (1) with large residual was omitted. The sextic distortion parameter H was not used in the fit; its omission may affect transition frequencies above about 500 GHz. The calculation may be accurate enough throughout.
¹⁴N hyperfine splitting matters in some astronomical observations. Therefore, a separate hyperfine calculation is provided for J' ≤ 12 below 120 GHz. NOTE: The partition function does take into account the spin multiplicity of the ¹⁴N nucleus !
The experimental dipole moment was published by
(4) M. Krüger, H. Dreizler, D. Preugschat, and D. Lentz, 1991, Angew. Chem. 103, 1674.