There are two stereoisomers of 1-cyano-1,3-butadiene, also known as 2,4-pentadienenitrile, Z and E. The energy order of the two is not known accurately, but the difference is likely small. They two species were thus treated as isolated species. Nevertheless, it is possible that the two forms will be found thermally equilibrated in space should their column densities be high enough.
The data were summarized by
(1) M. A. Zdanovskaia, P. M. Dorman, V. L. Orr, A. N. Owen, S. M. Kougias, B. J. Esselman, R. C. Woods, and R. J. McMahon, 2021, J. Am. Chem. Soc. 143, 9551.
The majority of the (millimeter) data is from that work. Additional microwave data are from
(2) 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.
Uncertainties used for the data from (1) are close to the implicitely used ones. The effects on the parameter values and uncertainties are very small.
The calculations are sufficiently accurate for all types of radio astronomical observations. Transition frequencies with calculated uncertainties exceeding 0.2 MHz should be viewed with caution.
The ¹⁴N hyperfine splitting is resolvable at lower frequencies or at lower quantum numbers. Therefore, a separate calculation with hyperfine structure is available up to 72 GHz with J up to 15.
The dipole moment is from a MP2 quantum-chemical calculation in by
(3) H. S. P. Müller, 2021 unpublished.