A λ2 mm molecular line survey of the C-star envelope IRC+10216

Abstract

The mm-wave spectrum of the C-star envelope IRC+10216 has been continuously surveyed between 129.0 and 172.5 GHz with the IRAM 30-m telescope. 380 lines are detected, of which 317 have been identied. The iden- tied lines arise from 30 dierent molecules and radicals which, in their vast majority, are not observed in hot and dense interstellar clouds such as Orion A or W3(OH). Actually, half of the molecular species identied in the mm-wave spectrum of IRC+10216 were rst observed in the course of this spectral survey. The new species include several carbon-chain molecules and radicals, as well as silicon and metallic compounds. They also include molecules containing rare isotopes of C, Mg, Si, S and Cl, whose elemental abundance ratios in the envelope are redetermined. We observe, in particular, four 13 C isotopomers of C4H, three of C3 Na nd HC 3N, and four doubly-substituted isotopomers of SiS and CS. 63 lines remain unidentied. Probably, a large fraction of those are rotational transitions inside the excited bend- ing states of the abundant species NaCN, C5H, and C6H. We can also expect some lines to be ground state transi- tions of poorly known silicon and metal compounds, such as the slightly asymmetrical top molecule SiCSi.