  The J,K = 1,0-0,0 rotational transition of phosphine (PH3) at 267 GHz has
been tentatively identified with a T_MB = 40 mK spectral line observed with the
IRAM 30-m telescope in the C-star envelope IRC+10216. A radiative transfer
model has been used to fit the observed line profile. The derived PH3 abundance
relative to H2 is 6 x 10^(-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 that
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, as
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.
