Detection of the CCP Radical ( X 2 Π r ) in IRC +10216: A New Interstellar Phosphorus-containing Species

Abstract

The CCP radical (X2Πr) has been detected in the circumstellar gas of IRC +10216, the fifth phosphorus-bearing molecule identified in interstellar space. This identification was made on the basis of new laboratory millimeter/submillimeter direct absorption measurements, conducted in the range 120-413 GHz. Four rotational transitions of this species were observed using the Arizona Radio Observatory (ARO) 12 m telescope on Kitt Peak at 2 and 3 mm in wavelength. Each transition consists of lambda-doublets, which are well-separated in frequency in IRC +10216; five of these eight possible lines of CCP were clearly detected, while the remaining three were contaminated by stronger emission from other species. The column density derived for CCP was Ntot= 1.2 × 1012 cm−2 and Trot = 21 K. Modeling of the line profiles suggests that CCP arises from an extended shell with a maximum radius of ~40''. The abundance of this radical, relative to H2, is f ~ 1 × 10−9—roughly comparable to that of PN and CP in this source. CCP may be produced from radical-radical reactions of CP, or ion-molecule chemistry involving P+ and HCCH. The identification of CCP is additional evidence that phosphorus chemistry is active in carbon-rich circumstellar gas.