The data have been summarized by
(1) H. S. P. Müller, S. Thorwirth, and F. Lewen, 2020, J. Mol. Struct. 1207, Art. No. 127769.
The submillimeter data and part of the millimeter data were taken from that work. Additional millimeter data were taken from
(2) A. Dubrulle, D. Boucher, J. Burie, and J. Demaison, 1978, J. Mol. Spectrosc. 72, 158. Two micowave transition frequencies were taken from
(3) R. Trambarulo, and W. Gordy, 1950, J. Chem. Phys. 18, 1613. The purely K-dependent parameters A, D_K, and an estimate of H_K, were taken from the main isotopic species as described in (1) based on ground state combination loops from
(4) H. S. P. Müller, P. Pracna, and V.-M. Horneman, 2002, J. Mol. Spectrosc. 216, 397.
The calculations should be sufficient for all observational purposes. Some caution may be advised for transitions having high values of J and K.
At low temperatures, it may be necessary to discern between A-¹³CH₃CCH and E-¹³CH₃CCH. 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-¹³CH₃CCH with K > 0 and all other states, respectively. The J_K = 1₁ level is the lowest E state level. It is 5.5855 cm^–1 above ground.
The dipole moment was assumed to agree with that of the main species from
(5) J. S. Muenter, and V. W. Laurie, 1966, J. Chem. Phys., 45, 855.