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The fit is largely based on
(1) A. M. Daly, C. Bermúdez, L. Kolesniková,
and J. L. Alonso,
2015, Astrophys. J. Suppl. Ser. 218, Art. No. 30.
At higher J and Ka, the transitions
are perturbed by the lowest excited vibrational state. Potentially
perturbed transitions were written into a separate file.
Remaining transition frequencies with residuals larger than
200 kHz were omitted.
Also included in the fit were data reported
by
(2) M. Winnewisser, G. Winnewisser, T. Honda, and E. Hirota,
1975, Z. Naturforsch. A 30, 1001.
Uncertainties close to the reported ones were used for these
data, which in turn include data from
(3) E. A. Cherniak and C. C. Costain,
1966, J. Chem. Phys. 45, 104.
The trans-conformer is lowest in energy. The higher
lying cis-conformer is much higher than several low-lying
vibrational states. The predictions should be reliable enough
for astronomical observations throughout.
No vibrational state and no other conformer were considered in
the calculation of the partition function.
The dipole moment was determined by
(4) C. E. Blom, G. Grassi, A. Bauder,
1984, J. Am. Chem. Soc. 106, 7427.
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