Anomalous absorption in c-C₃H and c-C₃D radicals^*

¹ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany e-mail: [kegel;sedlmayr]@astro.physik.tu-berlin.de
² School of Physical Sciences, S. R. T. M. University, Nanded 431 606, India e-mail: suresh492000@yahoo.co.in

Received: 14 June 2006
Accepted: 9 February 2007

Abstract

Context.The c-C₃H radical was first detected in TMC-1 by Yamamoto et al. (1987, ApJ, 322, L55), who observed the 2₁₂ 1₁₁ transition at 91.5 GHz in emission. Mangum & Wootten (1990, A&A, 239, 319) observed the 1₁₀ 1₁₁ transition at 14.8 GHz in emission in 12 additional galactic objects.

Aims.The aim of this investigation is a quantitative estimate of relative line intensities under NLTE conditions.

Methods.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.

Results.Our results show that the 3₃₁ 3₃₀ 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 1₁₀ 1₁₁ 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.