The molecule is nearly T-shaped with the NaN bond slightly shorter than the NaC bond. Therefore, the molecule should be considered more as sodium isocyanide rather than as sodium cyanide.
The first entry from Apr. 2007 has been revised based on an analysis from
(1) H. S. P. Müller, D. T. Halfen, and L. M. Ziurys, 2012, J. Mol. Spectrosc. 272, 23.
The experimental measurements were taken from
(2) J. J. van Vaals, W. L. Meerts, and A. Dymanus, 1984, Chem. Phys. 86, 147.
As described in (1), the reported uncertainties in (2) were assumed to be 3 σ values. The experimental data set is rather small. Nevertheless, the predictions should be fairly reliable as long as the predicted uncertainties do not exceed 0.5 MHz.
While in the laboratory b-type transitions have been observed, their intensities are likely very small because the b dipole moment component is about 1.5 orders of magnitude smaller than the a component; hence, transitions will be about three orders of magnitude weaker.
Hyperfine structure splitting caused by the ¹⁴N nucleus or the ²³Na nucleus are not of relevance for astronomical observations.
The dipole moment was assumed to be the same as for the main isotopic species, see e049510.cat.