Discovery of methyl silane and confirmation of silyl cyanide in IRC +10216.

We report the discovery in space of methyl silane, CHSiH, from observations of ten rotational transitions between 80 and 350 GHz ( from 4 to 16) with the IRAM 30 m radio telescope. The molecule was observed in the envelope of the C-star IRC +10216. The observed profiles and our models for the expected emission of methyl silane suggest that the it is formed in the inner zones of the circumstellar envelope, 1-40 , with an abundance of (0.5-1) × 10 relative to H. We also observed several rotational transitions of silyl cyanide (SiHCN), confirming its presence in IRC +10216 in particular, and in space in general. Our models indicate that silyl cyanide is also formed in the inner regions of the envelope, around 20 , with an abundance relative to H of 6×10. The possible formation mechanisms of both species are discussed. We also searched for related chemical species but only upper limits could be obtained.