Fulvene is a cyclic isomer of benzene. Transition frequencies were taken from
(1) M. C. McCarthy, K. L. K. Lee, P. B. Carroll, J. P. Porterfield, P. B. Changala, J. H. Thorpe, and J. F. Stanton, 2020, J. Phys. Chem. A 124, 5170.
One transition frequency with large residuals was omitted from the fit. An estimate of D_K was taken from a coupled cluster quantum-chemical calculation by
(2) S. Thorwirth, 2021, unpublished.
The data set is rather limited. The calculations were therefore truncated at 160 GHz and at J = 30. The calculations should be sufficient for searches in cold environments. Transition frequencies with calculated uncertainties exceeding 0.2 MHz should be viewed with caution as should be those having ΔK_a = 2.
Spin-statistical weight ratios of 9 : 7 for levels with K_a being odd and even, respectively, have been taken into account.
The dipole moment is from
(3) P. A. Baron, R. D. Brown, F. R. Burden, P. J. Domaille, and J. E. Kent, 1972, J. Mol. Spectrosc. 43, 401.