  We report the discovery in space of a disilicon species, SiCSi, from
observations between 80 and 350 GHz with the IRAM 30m radio telescope. Owing to
the close coordination between laboratory experiments and astrophysics, 112
lines have now been detected in the carbon-rich star CWLeo. The derived
frequencies yield improved rotational and centrifugal distortion constants up
to sixth order. From the line profiles and interferometric maps with the
Submillimeter Array, the bulk of the SiCSi emis- sion arises from a region of 6
arcseconds in radius. The derived abundance is comparable to that of SiC2. As
expected from chemical equilibrium calculations, SiCSi and SiC2 are the most
abundant species harboring a SiC bond in the dust formation zone and certainly
both play a key role in the formation of SiC dust grains.
