The experimental microwave line list was published by
(1) W. H. Styers, B. J. Esselman, S. A. Wood, P. B. Changala, G. H. Jones, M. C. McCarthy, J. F. Stanton, R. C. Woods, and R. J. McMahon, 2026, J. Am. Chem. Soc. 148, 14072.
The entry should be sufficient for all types of astronomical observations. Frequencies with calculated uncertainties excceding 0.1 MHz should be viewed with caution. At low temperatures, it may be necessary to discern between ortho-c-H₄C₃O and para-c-H₄C₃O. The ortho and para states are described by K_a even and odd, respectively. The nuclear spin-weights are 5 and 3 for ortho-c-H₄C₃O and para-c-H₄C₃O, respectively. The J_KaKc = 1₁₁ level is the lowest ortho level. It is 0.8681 cm^–1 above ground.
The dipole moment was determined in
(2) J. M. Pochan, J. E. Baldwin, and W. H. Flygare, 1968, J. Am. Chem. Soc. 90, 1072.