Very accurate microwave data were published by
(1) M. C. McCarthy, K. L. K. Lee, J. P. Porterfield, P. B. Changala, and A. K. Eckhardt, 2021, Mol. Phys. 119, Art. No. e1975052.
Additional lines are from
(2) R. D. Brown, K. G. Dyall, P. D. Godfrey, P. C. Elmes, and D. Mc Naughton, 1988, J. Am. Chem. Soc. 110, 789.
Some spectroscopic parameters were estimated from the main isotopolog by
(3) H. S. P. Müller, 2002, unpublished.
The calculations should be accurate enough for observations in cold sources. K_a = 0 and 1 may be reliable enough up to the 3 mm region. Transitions involving higher K_a should be viewed with increasing caution.
¹³C nuclear spin-rotation splitting may be resolvable in cold sources for K_a = 1. Therefore, a separate ¹³C hyperfine calculation is provided. Note: the spin multiplicity g_I of 2 for the ¹³C nucleus has been considered At low temperatures, it may be necessary to discern between ortho-H₂¹³CC₂S and para-H₂¹³CC₂S. The ortho states are described by K_a odd, the para states by K_a even. The nuclear spin-weights are 3 and 1 for ortho-H₂¹³CC₂S and para-H₂¹³CC₂S, respectively. The J_KaKc = 1₁₁ level is the lowest ortho level. It is approximately 9.6 cm^–1 above ground.
The dipole moment of the main isotopolog was taken from (2).