Astronomical detection of the cyanobutadiynyl radical C N

M. Guélin , N. Neininger , - J. Cernicharo
IRAM, 300 Rue de la piscine, F-38406 S Martin d'Hères, France
Radioastron. Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
Instituto de Estructura de la Materia, Madrid, Spain
Abstract: Despite chemical model predictions that C N and even longer cyanopolyyne radicals must be abundant in interstellar and circumstellar clouds, C N has escaped detection in space for more than 20 years. Following the recent ab initio quantum mechanical calculations, made by P. Botschwina (Chem. Phys. Lett. 259, 627, 1996), and the laboratory work of Y. Kasai et al. (ApJ, 477, L65, 1997), this elusive carbon-chain radical has been detected in the dark cloud TMC1 and tentatively detected in the circumstellar envelope IRC+10216 (Fig. 2). C N appears to be two orders of magnitude less abundant than the related molecule HC N and much less abundant than expected from current gas phase chemistry models. In comparison the HC N to C N abundance ratio is of the order of 10, in reasonable agreement with model predictions.

We have also detected in IRC+10216, next to C N, two lines arising from the C H radical in its excited bending state. The intensity ratio between the rotational transitions in the C H ground state and in the excited bending state, hence presumably the population ratio between these two states, is .

 
Figure 2: Spectrum observed with the 30-m telescope toward IRC+10216. The C H and C N line frequencies derived from laboratory measurements are indicated by downward arrows. The spectral resolution is 1 MHz (3.3 kms ).

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