2000A&A...363L...9G

We report the detection of the SiCN radical in an astronomical source, the envelope of the C star IRC +10216/CW Leo. The microwave spectrum of SiCN was recently studied by four of us in the laboratory and the rotational transition frequencies were accurately measured. The ground fine structure state, ²Π_1/2, has three rotational transitions, each with λ-doubling in the 80-116GHz atmospheric window (J=7.5->6.5, 8.5->7.5 and 9.5->8.5, at 83.0, 94.0, and 105.1 GHz). The three λ-doublets (six components) are detected at a level of 5 mK with the IRAM 30-m telescope. Judging from the cusped shape of the line profiles, SiCN is largely confined to the outer molecular envelope, like most other radicals. Its abundance relative to H₂ is estimated to be 4x10^–9, a factor of 20 lower than that of MgNC. The isoelectronic radical SiCCH was not detected. We confirm our previous tentative detections of the carbon chain H₂C₆ and of NP in IRC+10216.