With respect to the Sep. 2002 entry, a more extensive and more acurate line list has been provided in
(1) G. Cazzoli and C. Puzzarini, 2008, Astron. Astrophys. 487, 1197.
The purely K-dependent parameters (A and D_K), needed to obtain reasonable intensities, were taken from CH₃CCH;
(2) H. S. P. Müller, P. Pracna, and V.-M. Hornemann, 2002, J. Mol. Spectrosc., 216, 397.
The dipole moment is from
(3) M. Bester, K. M. T. Yamada, G. Winnewisser, W. Joentgen, H.-J. Altenbach, and E. Vogel, 1984, Astron. Astrophys. 137, L20.
At low temperatures, it may be necessary to discern between A-CH₃C₄H and E-CH₃C₄H. The A states are described by K = 3n, the E states by K = 3n ± 1. The nuclear spin-weight ratio is 2 : 1 for A-CH₃C₄H with K > 0 and all other states, respectively. The J_K = 1₁ state is the lowest E state. It is 5.3762 cm^–1 above ground.