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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.
Calculations of higher values of Ka
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 Ka odd,
the para states by Ka even.
The nuclear spin-weights are 3 and 1 for ortho-H2C2O
and para-H2C2O, respectively.
The JKaKc = 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
Ka = 1 plus the two J =
2 – 1 transitions along with separate
ortho partition function values.
The partition function values below refer to the ground
vibrational state only.
Vibrational correction factors have been derived for
the main isotopolog in the harmonic approximation
for a posteriori corrections of the column densities.
The dipole moment was reported in 2.
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