The experimental lines were taken from
(1) S. Saito, Y. Endo, M. Takami, and E. Hirota, 1983, J. Chem. Phys. 78, 116;
and from
(2) I. Morino, K. M. T. Yamada, S. P. Belov, G. Winnewisser, and E. Herbst, 2000, Astrophys. J. 532, 377.
The constants used in the fit are essentially those of (2).
Predictions with uncertainties up to about 1 MHz should be reliable.
The dipole moment was taken from (1). Magnetic dipole transitions were predicted, too.