Microwave data were taken from
(1) S. S. Butcher, 1965, J. Chem. Phys. 42, 1830;
and from
(2) G. Luss and M. D. Harmony, 1965, J. Chem. Phys. 43, 3768.
Initial estimates of the quartic distortion parameters were taken from an MP2 quantum-chemical calculation by
(3) H. S. P. Müller, 2021, unpublished.
The data set is quite limited, the calculations were therefore truncated at 120 GHz and at J = 20. The calculations should be sufficient for searches in cold environments. Transition frequencies with calculated uncertainties exceeding 0.2 MHz should be viewed with caution.
Spin-statistical weight ratios have been ignored because of the proximity to 1 : 1.
The dipole moment was determined in (1).