Spectroscopic parameters for silacyclopropynylidene, SiC2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite

► SiC2 is an abundant molecule in circumstellar shells of carbon-rich late-type stars. ► Lines have been detected beyond 1 THz in astronomical observations of CW Leo. ► The positions were not well predicted by parameters from laboratory data. ► Combining laboratory and astronomical data improved greatly spectroscopic parameters.