2007A&A...467..371C

The c-C₃H radical was first detected in TMC-1 by Yamamoto et al. (1987ApJ...322L..55Y), who observed the 2_1 2_–>11 1_ transition at 91.5 GHz in emission. Mangum & Wootten (1990A&A...239..319M) observed the 1_1 0_–>11 1_ transition at 14.8 GHz in emission in 12 additional galactic objects. The aim of this investigation is a quantitative estimate of relative line intensities under NLTE conditions. For wide ranges of physical parameters, where these molecules may be found, we have solved a set of statistical equilibrium equations coupled with the equations of radiative transfer in an on-the-spot approximation. For c-C₃H, we accounted for 51 energy levels connected by 207 radiative transitions, and for c-C₃D, we accounted for 51 energy levels connected by 205 radiative transitions. Our results show that the 3_3 1_–>33 0_ transition of c-C₃H and c-C₃D may be found in absorption against the cosmic microwave background (CMB). Furthermore, we found population inversion for the 1_1 0_–>11 1_ transition. These findings may be useful in identifying these molecules in other cosmic objects, as well as for the determination of physical parameters in these objects.