Two low J transition frequencies were taken from astronomical observations by
(1) J. Cernicharo, B. Tercero, C. Cabezas, M. Agúndez, E. Roueff, R. Fuentetaja, N. Marcelino, and P. de Vicente, 2024, Astron. Astrophys. 682, L13.
The D value was kept fixed to the value of the main isotopolog scaled by the square of the ratio of the B values. The calculation may be accurate enough throughout, but some caution is advised.
¹⁴N hyperfine splitting matters at most for transitions with very low values of J and was neglected in the present entry. Hence, the partition function does not take into account spin multiplicities of the ¹⁴N or ¹³C nuclei !
The dipole moment of the main isotopolog is from a quantum chemical calculation by
(2) P. Botschwina, M. Horn, S. Seeger, and J. Flügge, 1992, Chem. Phys. Lett. 195, 427.