With respect to the Jan. 2003 entry, very accurate (Lamb-dip) transition frequencies up to 717 GHz as well as additional accurate lines between 1.0 and 1.2 THz have been published by
(1) G. Cazzoli and C. Puzzarini, 2008, Astron. Astrophys. 487, 1197.
Additional high-K lines between 509 and 715 GHz as well as transition frequencies betwen 765 and 922 GHz were taken from
(2) H. S. P. Müller, S. Thorwirth, L. Bizzocchi, and G. Winnewisser, 2000, Z. Naturforsch. 55a, 491; and
(3) H. S. P. Müller, P. Pracna, and V.-M. Horneman, 2002, J. Mol. Spectrosc. 216, 397.
Ground state combination loops in (3) permit A and D_K to be determined. The data have been subjected to a combined fit with the ν₁₀ band data and the v₁₀ = 1 pure rotational data from (3) and references therein. The interactions of v₁₀ = 1 with v₉ = 1 and v₁₀ = 2, as described in (3), have been taken into account.
Experimental lines with uncertainties larger than 100 kHz have not been merged because of the many lines with smaller uncertainties.
The dipole moment is from
(4) P. M. Burrell, E. Bjarnov, and R. H. Schwendeman, 1980, J. Mol. Spectrosc., 82, 193.
At low temperatures, it may be necessary to discern between A-CH₃CCH and E-CH₃CCH. The A state levels are described by K = 3n, those of E state by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-CH₃CCH with K > 0 and all other states, respectively. The J_K = 1₁ level is the lowest E state level. It is 5.5933 cm^–1 above ground.
Besides the ground vibrational state, the partition function takes into account the states v₁₀ = 1, v₉ = 1, and v₁₀ = 2. Their respective contributions are given in parentheses as long as they are different from 0 within the quoted digits.