Frequencies without hyperfine splitting have been reported in
(1) A. J. Alexander, H. W. Kroto, and D. R. M. Walton, 1976, J. Mol. Spectrosc. 62, 175 and in
(2) L. Bizzocchi, C. Degli Esposti, and P. Botschwina, 2004, J. Mol. Spectrosc. 225, 145.
Transitions involving ¹⁴N hyperfine splitting were reported in
(3) M. E. Sanz, M. C. McCarthy, and P. Thaddeus, 2005, J. Chem. Phys. 122, Art. No. 194319.
¹⁴N hyperfine splitting may be resolved at low values of J. However, even at low temperatures these transitions are expected to be too weak. The partion function does not take into account hyperfine splitting and no vibrational contributions !
The dipole moment was assumed to be the same as that of the main species, see e075503.cat.