The phosphapropynylidyne radical, CCP, has been detected in five lines of four rotational transitions in the 3 and 2 mm regions:
D. T. Halfen, D. J. Clouthier, and L. M. Ziurys,
Detection of the CCP Radical (X <sup>2</sup>Π<sub>r</sub>) in IRC +10216: A New Interstellar Phosphorus-containing Species
Astrophys. J. 677, L101–L104 (2008).
The e λ-doubling component is overlapped by stronger featueres for the first three transitions; the f component seems to be unaffected for all four transitions.
Contributor(s): H. S. P. Müller; 03, 2008