(1) K. Bolton, D. G. Lister, and J. Sheridan, 1974, J. Chem. Soc. Faraday Trans. 2 70, 113
determined the s-trans conformer to be higher than the s-cis conformer by 58 (17) cm^–1 or 0.7 (2) kJ/mol or 83 (24) K.
The experimental data were taken from (1) and from
(2) C. Calabrese, A. Vigorito, G. Feng, L. B. Favero, A. Maris, S. Melandri, W. D. Geppert, and W. Caminati, 2014, J. Mol. Spectrosc. 295, 37.
With respect to the first entry of Dec. 2013, extensive microwave and millimeter wave data were added. These were published by
(3) E. R. Alonso, L. Kolesniková, I. Peña, S. T. Shipman, B. Tercero, J. Cernicharo, and J. L. Alonso, 2015, J. Mol. Spectrosc. 316, 84.
Uncertainties of individual data sets were tested and adjusted if necessary. A small number of transitions with large residuals from (3) were omitted. These were almost exclusively transitions with Δ(K_a > 0. Moreover, the number of spectroscopic parameters was reduced with respect to that work. An estimate of H_K was kept fixed in the fit. The calculations should be sufficient for all observational purposes. Transitions with calculated uncertainties larger than 0.1 MHz should be viewed with caution.
The partition function values were calculated summing up the ground state contributions of both conformers. The uncertainty of the energy of the trans conformer leads to some probably modest uncertainty in the partition function and to uncertainties in the relative intensities between the conformers, in particular at low temperatures.
The dipole moment components were measured in (1).