Astronomical detection of the cyanobutadiynyl radical C5N
  We report the detection of the elusive carbon-chain radical C5N in the dark cloud TMC1 and its tentative detection in the circumstellar envelope IRC+10216. C5N appears to be two orders of magnitude less abundant than the related molecule HC5N and much less abundant than expected from current gas phase chemistry models. In comparison the HC3N to C3N abundance ratio is of the order of 10, in reasonable agreement with model predictions.   We have also detected in IRC+10216 two lines arising from the C3H radical in its excited nu_4=1 state. 
M. Guelin, N. Neininger, J. Cernicharo