The experimental frequencies have been reported by
(1) E. Hirota, R. Sugisaki, C. J. Nielsen, and G. O. Sørensen, 1974, J. Mol. Spectrosc. 49, 251;
by
(2) E. M. Moskienko and S. F. Dyubko, 1991, Radiophys. Quant. Electr. 34, 181;
by
(3) E. M. Vorob'eva and S. F. Dyubko, 1994, Radiophys. Quant. Electr. 37, 155;
by
(4) A. V. Kryvda, V. G. Gerasimov, S. F. Dyubko, E. A. Alekseev, R. A. Motiyenko, 2009, J. Mol. Spectrosc. 254, 28;
and by
(5) R. A. Motiyenko, B. Tercero, J. Cernicharo, and L. Margulès, 2012, Astron. Astrophys. 548, Art. No. A71.
Please note: the data used in (1) were taken from
(6) C. J. Nielsen, 1973, PhD thesis, Københavns Universitet, Denmark.
Claus Nielsen and Matt Johnson are thanked for providing the data from (6).
All data were used with ¹⁴N hyperfine splitting as far as it had been resolved. The spectroscopic parameters of eighth order are scaled values from the ground vibrational state. Predictions with uncertainties larger than 1 MHz should be viewed with caution. This is probably not a limitation for any astronomical observations.
Please note: The partition function values refer to the ground vibrational state only ! Vibrational contributions to the partition function will be provided in the future. The wagging mode ν₁₂ is very anharmonic, so a classical estimation will be very incorrect.
The dipole moment was assumed to agree with that in the ground vibrational state, which was determined by
(7) R. J. Kurland and E. B. Wilson, 1957, J. Chem. Phys. 27, 585.