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Dimethylenecyclobutene is a cyclic isomer of benzene.
Transition frequencies were taken from
(1) R. D. Brown, P. D. Godfry, B. T. Hart, A. L. Ottrey,
M. Onda, and M. Woodruff,
1983, Aust. J. Chem. 36, 639.
Estimates of the quartic distortion parameters were
taken from an MP2 quantum-chemical calculation
by
(2) H. S. P. Müller, 2021, unpublished.
The data set is very limited. The calculations
were therefore truncated at 200 GHz and at
J = 50.
The calculations should be sufficient for searches
in cold environments. Transition frequencies with
calculated uncertainties exceeding 0.05 MHz
should be viewed with caution.
Spin-statistical weight ratios of 9 : 7 for levels
with Kc + Kc
being odd and even, respectively,
have been taken into account.
The dipole moment is from
(3) R. D. Brown, F. R. Burden, A. J. Jones,
and J. E. Kent,
1967, Chem. Comm. (London) 808.
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