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

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 identified. The identified lines arise from 30 different 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 identified in the mm-wave spectrum of IRC+10216 were first 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 C-13 isotopomers of C4H, three of C3N and HC3N, and four doubly-substituted isotopomers of SiS and CS. 63 lines remain unidentified. Probably, a large fraction of those are rotational transitions inside the excited bending states of the abundant species NaCN, C5H, and C6H. We call also expect some lines to be ground state transitions of poorly known silicon and metal compounds, such as the slightly asymmetrical top molecule SiCSi.