The gauche conformer is about 58 K lower than the anti conformer and is doubly degenerate with respect to the latter. It has no symmetry (C₁) 30 vibrational modes with v₂₈ = 1 being fourth lowest in energy. The transition frequencies were taken from
(1) H. S. P. Müller, A. Walters, N. Wehres, A. Belloche, O. H. Wilkins, D. Liu, R. Vicente, R. T. Garrod, K. M. Menten, F. Lewen, and S. Schlemmer, 2016, Astron. Astrophys., 595 Art. No. A87.
¹⁴N hyperfine splitting as well as CH₃ are unlikely to be resolved in astronomical observations.
The predictions may be sufficient for astronomical observations, but should be viewed with caution if the uncertainties are larger than 0.3 MHz. Predictions of b-type transitions should be viewed with caution, especially if K_a ≥ 3.
Note: the statistical weight of the anti and gauche conformers is 1 : 2 because of symmetry. We have estimated vibrational corrections in the harmonic oscillator approximation using fundamental vibrations of the gauche-conformer from
(2) J. R. Durig, B. R. Drew, A. Komer, and S. Bell, 2001, Phys. Chem. Chem. Phys., 3 766,
as commented in (1). Additional information on vibrational states is also available.
The dipole moment components were assumed to agree with those in the ground vibrational state of the respective conformer, see e069505.cat.