Ethanethiol, aka ethyl mercaptan, occurs in two distinguishable conformers because of the orientation of the SH group. The internal rotation of the CH₃ group can be neglected in most instances. The doubly degenerate gauche conformer is lowest in energy, the anti conformer is higher in energy by about 160 K. This is an average value of several reported ones. Tunneling between the two equivalent gauche conformers lifts the degeneracy, causing a gauche⁺ and a gauche^– state which interact heavily.
The spectroscopic parameters were published by
(1) H. S. P. Müller, A. Belloche, L.-H. Xu, R. M. Lees, R. T. Garrod, A. Walters, J. van Wijngaarden, F. Lewen, S. Schlemmer, and K. M. Menten, 2016, Astron. Astrophys. 587, Art. No. A92.
Initial data are from
(2) R. E. Schmidt and C. R. Quade, 1975, J. Chem. Phys. 62, 3864.
Additional, rather extensive data are from
(3) L. Kolesniková, B. Tercero, J. Cernicharo, J. L. Alonso, A. M. Daly, B. P. Gordon, and S. T. Shipman, 2014, Astrophys. J. 784, Art. No. L7.
Predictions should be sufficiently accurate for all observational purposes. Uncertainties concerning the signs of the main interaction parameters with respect to those of the dipole moment components appears to have only minute effects on the intensities.
The partition function does not takes into account the anti conformer !
The dipole moment was determined in (2).