The experimental data was reported by
(1) J. M. Vrtilek, C. A. Gottlieb, E. W. Gottlieb, T. C. Killian, and P. Thaddeus, 1990, Astrophys. J. 364, L53.
The predictions, in particular at higher J or K_a, should be viewed with some caution.
The dipole moment is from a quantum chemical calculation.
At low temperatures, it may be necessary to discern between ortho-l-C₃H₂ and para-l-C₃H₂. 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-l-C₃H₂ and para-l-C₃H₂, respectively. The J_KaKc = 1₁₁ is the lowest ortho state. It is 9.9720 cm^–1 above ground.