The first entry from Dec. 2009/May 2011 was already rather extensive and almost guaranteed to be sufficient for radio astronomical observations.
(1) L. Nguyen, A. Walters, L. Margulès, R. A. Motiyenko, J.-C. Guillemin, C. Kahane, and C. Ceccarelli,
2013, Astron. Astrophys. 553, Art. No. A84;
published additional data between 480 and 940 GHz employing an isotopically enriched sample. With respect to earlier measurements in (2), they report mainly more accurate and more extensive data which also extend to higher K_a. Some of the higher K_a data were already excluded from the fit in (1) because of suspected perturbations with one or more low-lying vibrational states. Here, all data above K_a = 14 were omitted, resulting in a somewhat different parameter set.
(2) H. S. P. Müller, B. J. Drouin, and J. C. Pearson, 2009, Astron. Astrophys. 506, 1487;
provide additional data between 277 and 1197 GHz. Further data were taken from
(3) M. Le Guennec, G. Wlodarczak, J. Burie, and J. Demaison, 1992, J. Mol. Spectrosc. 154, 305;
and three microwave lines from
(4) L. F. Thomas, E. J. Sherrard, and J. Sheridan, 1955, Trans. Faraday Soc. 51, 619.
The low symmetry of the molecule causes a small b-dipole moment component. Some of the corresponding transitions were observed in (1) and (3). The predictions are reliable up to about K_a = 14.
Note: Non-trivial spin-statistics do not matter for this low symmetry (C_S) isotopolog.
Note also that under LTE conditions excited vibrational states should be observable before K_a = 10 is.
The dipole moment has been derived from the main isotopolog, see e041505.cat, taking into account the rotation of the inertial axes. The magnitude of the b-component should be taken with some care.