The experimental frequencies have been reported by
(1) C. J. Nielsen, 1973, PhD thesis, Københavns Universitet, Denmark;
and from
(2) A. S. Kutsenko, R. A. Motiyenko, L. Margulès, and J.-C. Guillemin, 2013, Astron. Astrophys. 549, Art. No. A128.
Claus Nielsen and Matt Johnson are thanked for providing the data from (1).
The data from (2) were provided as if they showed ¹⁴N hyperfine splitting, though this applies only to a part of the data. Because of the extensive data set, no adjustements were made at present. Moreover, the data from (1) were treated accordingly, and no lines have been merged. Nevertheless, all experimental data can be viewed as recommended, though calculated frequencies should be prefereed in cold astronomical sources. Three diagonal octic distortion parameters were estimated by scaling values from HC(O)NH₂ and DC(O)NH₂.
Predictions with uncertainties larger than 0.5 MHz should be viewed with caution. This is unlikely to be a limitation for any astronomical observations.
¹⁴N hyperfine splitting may be resolved for low values of J. Therefore, a separate hyperfine calculation is provided for J" = J' ≤ 10 and frequencies below 200 GHz. HFS caused by the D nucleus has not been resolved in the laboratory and is not likely to be resolved in astronomical sources.
The partition function includes the ¹⁴N spin mulitiplicity. Vibrational contributions to the partition function will be provided in the future.
The dipole moment was assumed to agree with that of the main isotopolog, which was determined by
(3) R. J. Kurland and E. B. Wilson, 1957, J. Chem. Phys. 27, 585.