Spectroscopic parameters for silacyclopropynylidene, SiC$_2$, from
  extensive astronomical observations toward CW Leo (IRC +10216) with the
  Herschel satellite
  A molecular line survey has been carried out toward the carbon-rich
asymptotic giant branch star CW Leo employing the HIFI instrument on board of
the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could
be assigned unambiguously to the fairly floppy SiC$_2$ molecule. However,
predictions from laboratory data exhibited large deviations from the observed
frequencies even after some lower frequency data from this survey were
incorporated into a fit. Therefore, we present a combined fit of all available
laboratory data together with data from radio-astronomical observations.
