Ketenyl is a planar molecule with a low barrier to linearity, i.e. it is quasilinear. The fine structure splitting is rather difficult to model, such that only K_a = 0 data were considered in the present calculation. This should be sufficient for astronomical observations because the molecule was found in dark cloud environments only thus far. The lines were taken from
(1) Y. Endo and E. Hirota, 1987, J. Chem. Phys. 86, 4319.
The N = 1 – 0 transition was recorded with resolved hyperfine structure by
(2) Y. Ohshima and Y. Endo, 1993, J. Mol. Spectrosc. 159, 458.
With respect to the first entry from July 2012, additional transition frequencies were taken from
(3) J. Chantzos, S. Spezzano, C. Endres, L. Bizzocchi, V. Lattanzi, J. Laas, A. Vasyunin, and P. Caselli, 2019, Astron. Astrophys. 621, Art. No. A111.
Calculations were limited to 600 GHz; see also DCCO entry, e042519.cat. These data should be sufficient and accurate.
The ab initio dipole moment was reported by
(4) P. G. Szalay, G. Fogarasi, L. Nemes, 1996, Chem. Phys. Lett. 263, 91. Only the total dipole moment was given, but it is expected to be only marginally larger than the a component. The b component is very much smaller, and the origin of corresponding transitions is near 1.2 THz with a large uncertainty of several tens of gigahertz.