2008A&A...485L..33A

The J_K=1₀-0₀ rotational transition of phosphine (PH₃) at 267GHz has been tentatively identified with a T_MB∼40mK spectral line observed with the IRAM 30-m telescope in the C-star envelope IRC +10216. A radiative transfer model was used to fit the observed line profile. The derived PH₃ abundance relative to H₂ is 6x10^–9, although it may have a large uncertainty due to the lack of knowledge about the spatial distribution of this species. If our identification is correct, it implies that PH₃ has a similar abundance to what is reported for HCP in this source and that these two molecules (HCP and PH₃) together take up about 5% of phosphorus in IRC +10216. The abundance of PH₃, like that of other hydrides in this source, is not well explained by conventional gas-phase LTE and non-LTE chemical models, and may imply formation on grain surfaces.