Transition frequencies with hyperfine splitting were taken from
(1) N. Heineking, J.-U. Grabow, and W. Stahl, 1994, Mol. Phys. 140, 62.
Extensive millimeter data were taken from
(2) L. Kolesniková, E. R. Alonso, B. Tercero, J. Cernicharo, and J. L. Alonso, 2018, Astron. Astrophys. 611, Art. No. A173.
The parameter set differs slightly from that in (2). The spectrum is not well described by a conventional Hamiltonian. While the reason was not determined, it may be related to a very low lying vibrational mode. The higher K_a the lower the maximum J value in the fit. The entry was truncated at 370 GHz, but we recomment to use rely only on measured data.
The dipole moment components were determined by
(3) T. Sakaizumi, O. Yamada, K. Ushida, O. Ohashi, I. Yamaguchi, 1976, Bull. Chem. Soc. Japan 49, 2908.