The entry refers to the E- or trans-conformer, which is by far lowest in energy. The data set was taken from
(1) N. Jiang, M. Melosso, L. Bizzocchi, S. Alessandrini, J.-C. Guillemin, L. Dore, and C. Puzzarini, 2022, J. Phys. Chem. A 126, 1881.
New millimeter wave data were reported between 229 and 331 GHz. Data below 50 :GHz were taken from
(2) M. Sugie, H. Takeo, and C. Matsumura, 1989, J. Am. Chem. Soc. 111, 906.
The accuracy of the entry should be sufficient for astronomical observations. Transition frequencies with calculated uncertainties exceeding 0.1 MHz should be viewed with caution.
¹⁴N hyperfine splitting may matter in astronomical observations. Therefore, a separate hyperfine calculation is provided for J ≤ 40 and K_a ≤ 4 below 400 GHz and with somewhat lowered intensity cut-offs. NOTE: The partition function takes into account the spin multiplicity of the ¹⁴N nucleus !
The dipole moment was measured in (2).