The microwave frequencies have been reported by
(1) M. C. McCarthy, L. Zou, and M.-A. Martin-Drumel, 2017, J. Chem. Phys. 146, Art. No. 154301.
The parameter set is slightly different from the one in (1). In addition, most reported uncertainties were deemed to be slightly conservative; they have been adjusted. No b-type transitions were recorded experimentally, so none were predicted. Predictions were truncated at J = 50 and K_a = 1 because of limitations in the experimental data. Larger quantum numbers were accessed for the determination of the partition function. The predictions may well be sufficient for the identification of the molecule in dark clouds. Predictions with uncertainties larger than 0.05 MHz should be viewed with caution.
The dipole moment is from an ab initio calculation in (1).