Yamamoto et al. (1987) reported the first detection of c-C3H radical in {TMC-1} through its transition 212→111 at 91.5 GHz. Mangum and Wootten (1990) detected c-C3H through the transition 110→111 at 14.8 GHz in 12 additional galactic objects. The column density of c-C3H in the objects was estimated to be about one order of magnitude lower than that of the C3H2 which is ubiquitous in the galactic objects. The most probable production mechanism of both the C3H and C3H2 in dark clouds is a common dissociation reaction of C3H3+ ion (Adams & Smith, 1987). Although the c-C3H is 0.8 eV less stable than its isomer l-C3H, finding of comparable column densities of both the isomers in {TMC-1} supports the idea of comparable formation of both the c-C3H and l-C3H in the cosmic objects. Existence of a metaisomer in interstellar condition is a well known phenomenon in astronomy. We propose that c-C3H may be identified through the transition 331→330 at 3.4 GHz in absorption against the cosmic 2.7 K background in dense cosmic objects when no strong source is present in the background. When there is some strong source in the background of the object, peak of the absorption line decreases with the increase of the strength of the background source. However, at low densities, the intensity is found to increase. Hence, in low density regions, a background source can help in detection of the line. This absorption line may play an important role for identification of c-C3H in a large number of cosmic objects. Similar absorption features are found for c-C3D radical also.
@article{arxiv.astro-ph/0305324,
title = {Anomalous Absorption in Cyclic C$_3$H Radical},
author = {Suresh Chandra and S. A. Shinde},
journal= {arXiv preprint arXiv:astro-ph/0305324},
year = {2007}
}