The experimental data was reported by
(1) C. A. Gottlieb, T. C. Killian, P. Thaddeus, P. Botschwina, J. Flügge, and M. Oswald, 1993, J. Chem. Phys. 98, 4478; and from
(2) M. C. Mc. Carthy and P. Thaddeus, 2002, J. Mol. Spectrosc. 211, 235.
The predictions, in particular at higher J or K_a, should be viewed with some caution. ¹³C nuclear spin-rotation splitting may be resolvable at low values of J. Respective data are from (2).
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 approximately 9.966 cm^–1 above ground.