The branched 3-methylbutyronitrile, also known as iso-butyl cyanide, exists in two different conformations, anti and gauche, which are isoenergetic within quite small uncertainties, as was shown from relative intensity measurements of rotational transitions. Their frequencies were reported by
(2) N. Wehres, M. Hermanns, O. H. Wilkins, K. Borisov, F. Lewen, J.-U. Grabow, S. Schlemmer, and H. S. P. Müller, 2018, Astron. Astrophys., 615 Art. No. A140.
¹⁴N hyperfine structure was resolved for several transitions.
Predictions with uncertainties much larger than 0.15 MHz should be viewed with caution. This should not be any limitation for astronomical observations.
¹⁴N hyperfine structure is unlikely to be resolved in astronomical observations.
Note: The partition function includes contributions from the gauche conformer. Vibrational correction factors are available for a posteriori correction.
The dipole moment components are from an ab calculation in (1).