Rotational spectroscopy of isotopic cyclopropenone, $c$-H$_2$C$_3$O, and
  determination of its equilibrium structure
  Cyclopropenone was first detected in the cold and less dense envelope of
Sagittarius B2(N). It was found later in several cold dark clouds and it may be
possible to detect its minor isotopic species in these environments. In
addition, the main species may well be identified in warmer environments. We
aim to extend existing line lists of isotopologs of c-H2C3O from the microwave
to the millimeter region and create one for the singly deuterated isotopolog to
facilitate their detections in space. Furthermore, we aim to extend the line
list of the main isotopic species to the submillimeter region and to evaluate
an equilibrium structure of the molecule. We employed a cyclopropenone sample
in natural isotopic composition to investigate the rotational spectra of the
main and 18O-containing isotopologs as well as the two isotopomers containing
one 13C atom. Spectral recordings of the singly and doubly deuterated isotopic
species were obtained using a cyclopropenone sample highly enriched in
deuterium. We recorded rotational transitions in the 70-126 GHz and 160-245 GHz
regions for all isotopologs and also in the 342-505 GHz range for the main
species. Quantum-chemical calculations were carried out to evaluate initial
spectroscopic parameters and the differences between ground-state and
equilibrium rotational parameters in order to derive semi-empirical equilibrium
structural parameters. We determined new or improved spectroscopic parameters
for six isotopologs and structural parameters according to different structure
models. The spectroscopic parameters are accurate enough to identify minor
isotopic species at centimeter and millimeter wavelengths while those of the
main species are deemed to be reliable up to 1 THz. Our structural parameters
differ from earlier ones. The deviations are attributed to misassignments in
the earlier spectrum of one isotopic species.
