The branched isomer of 2-cyanomethane, also known as sec-butyl cyanide or 2-methylbutyronitrile, exists in three different conformations. Low-resolution infrared spectroscopy and molecular mechanics calculations were reported by
(1) G. A. Crowder and G. O. Carlisle, 1991, J. Comput. Chem., 12, 880.
The anti-conformer was found to be lowest in energy. The gauche- and gauche'-conformers, with the terminal methyl group rotated by about 120^o and about –120^o, respectively, are about 249 and 283 cm^–1 higher in energy. The transitions were reported by
(2) H. S. P. Müller, O. Zingsheim, N. Wehres, J.-U. Grabow, F. Lewen, and S. Schlemmer, 2017, J. Phys. Chem. A, 121 7121.
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 does not include contributions from other vibrations or conformers. Respective information for a posteriori corrections will be provided in the future.
The dipole moment components are from an ab calculation in (2).