Spiro[2.4]hepta-4,6-diene is an isomer of toluene consisting of two cycles fused at one C. Transition frequencies were taken from
(1) S. W. Staley, A. E. Howard, M. D. Harmony, S. N. Mathur, M. Kattija-Ari, J.-I. Choe, and G. Lind. 1980, J. Am. Chem. Soc. 102, 3639.
Initial 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(2) H. S. P. Müller, 2021, unpublished.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 quite limited. The calculations were therefore truncated at 200 GHz and at J = 60. The calculations should be sufficient for searches in cold environments. Transition frequencies with calculated uncertainties exceeding 0.1 MHz should be viewed with caution.
Spin-statistical weight ratios have been ignored because of the proximity to 1 : 1.
The dipole moment is from (1).