syn-3-Butenenitrile is lower in energy than gauche-3-butenenitrile. The conversion does not require a formal rotation around a double bond. Therefore, the two species should be considered as conformers. There are two equivalent gauche-configurations separated by the anti-transition state. Experimental results by
(1) J. R. Durig, G. A. Guirgis, and A. S. Drew, 1994, J. Raman. Spectrosc. 25, 907
suggest gauche to be higher than syn by 336 ± 61 cm^–1 in the gas phase. However, since gauche was also detected in a cold environment, it is necessary to treat the two conformers separately.
The millimeter data were taken from
(2) J. Demaison, J. Burie, D. Boucher, and G. Wlodarczak, 1991, J. Mol. Spectrosc. 146, 455.
Also included in the fit were microwave transitions from
(3) M. C. McCarthy, K. L. K. Lee, P. B. Carroll, J. P. Porterfield, P. B. Changala, J. H. Thorpe, and J. F. Stanton, 2020, J. Phys. Chem. A 124, 5170.
Some additional spectroscopic parameters were used, in part estimated. The calculation should be suitable for most observational purposes. Transition frequencies with calculated uncertainties exceeding 0.2 MHz should be viewed with caution.
The ¹⁴N hyperfine splitting can be resolved for low values of J. Therefore, a separate hyperfine calculation is provided up to J' = 25 and up to 120 GHz. Please note that the ¹⁴N spin multiplicity was also considered in the hyperfine free calculation.
Please note: the quantum number range in the HFS file has been extended in April 2024 so that a-type transitions occur at higher frequencies; a partition function value in the intensity file was also corrected.
The dipole moment components are from
(4) K. V. L. N. Sastry, V. M. Rao, and S. C. Dass, 1968, Can. J. Phys. 46, 959.