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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 Ka = 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;
and from
(2) 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 450 GHz because the
J = N – 0.5 fine structure component
is increasingly poorly reproduced, possibly because of
neglect of the asymmetry of the molecule. Nevertheless,
these data should be sufficient and accurate.
The ab initio dipole moment of HCCO 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.
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