The lines were taken from
(1) H. R. Johnson and M. W. P. Strandberg, 1952, J. Chem. Phys. 20, 687;
(2) B. Fabricant, D. Krieger, and J. S. Muenter, 1977, J. Chem. Phys. 67, 1576;
and (3) R. D. Brown, P. D. Godfrey, D. McNaughton, A. P. Pierlot, and W. H. Taylor, 1990, J. Mol. Spectrosc. 140, 340.
Transition frequencies by T. Y Wang, K. M. T. Yamada, and L. Nemes, which were used in
(4) J. W. C. Johns, L. Nemes, K. M. T. Yamada, T. Y Wang, J. L. Domenech, J. Santos, P. Cancio, D. Bermejo, J. Ortigoso, and R. Escribano, 1992, J. Mol. Spectrosc. 156, 501,
were kindly communicated by L. Nemes.
The 1₀₁ – 0₀₀ line was taken from
(5) D. H. Sutter and H. Dreizler, 2000, Z. Naturforsch. 55a, 695.
Additional lines used in
(6) A. Guarnieri and A. Huckauf, 2003, Z. Naturforsch. 58a, 275,
were kindly communicated by A. Huckauf.
Some higher order centrifugal distortion constants were kept fixed to values from 4. Predictions fot higher values of K_a should be viewed with caution.
At low temperatures, it may be necessary to discern between ortho-H₂C₂O and para-H₂C₂O. 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-H₂C₂O and para-H₂C₂O, respectively. The J_KaKc = 1₁₁ level is the lowest ortho level. It is 9.7395 cm^–1 above ground.
Dec. 2011: Separate para and ortho predictions are available along with separate para and ortho partition function values. Note: the spin-weight of 3 for the separate ortho predictions has been eliminated.
The ¹H hyperfine splitting may be resolved at low temperatures, low frequencies, and for low values of J. Therefore, a separate hyperfine calculation is provided up to J = 9 for transitions with ΔJ = 0 and K_a = 1 plus the two J = 2 – 1 transitions along with separate ortho partition function values.
The dipole moment was reported in 2.