Transition frequencies, largely from the microwave region, were taken from
(1) M. Sugie, H. Takeo, and C. Matsumura, 1989, J. Am. Chem. Soc. 111, 906.
The calculation was truncated at J = 40 and 120 GHz. The accuracy of the entry should be sufficient for observations in cold sources. 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 ≤ 10 below 120 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).