IRC+10216 as a spectroscopic laboratory

New data on the rotational lines of these species between 70 and 350GHz have been obtained with high spectral resolution (195kHz) with the IRAM 30m telescope in the direction of the circumstellar envelope IRC+10216. Frequency measurements can reach an accuracy of 50kHz for features observed with a good signal to noise ratio.

From the observed astrophysical lines and the available laboratory data new rotational and centrifugal distortion constants have been derived for all the isotopologues of SiC_2_, allowing to predict their spectrum with high accuracy in the millimeter and submillimeter domains. Improved rotational and centrifugal distortion constants have also been obtained for disilicon carbide, Si_2_C. This work shows that observations of IRC+10216 taken with the IRAM 30m telescope, with a spectral resolution of 195kHz, can be used for any molecular species detected in this source to derive, or improve, its rotational constants.