On the Detection of Circumstellar Silicon Carbide, SiC

Silicon carbide, SiC, has an inverted 3Π ground electronic state. The low-lying Ω = 2 component shows negligible Λ-doubling. The Ω = 1 and 0 components are about 60 amd 120 K higher in energy, respectively, and show substantial Λ-doubling.
SiC has been detected thus far only in the circumstellar envelope of CW Leo, also known as IRC +10216. 3, 3, and 1 components were detected for the J" = 1, 3, and 5 transitions near 80, 160, and 240 GHz covering all fine structure components by
J. Cernicharo, C. A. Gottlieb, M. Guélin, P. Thaddeus, and J. M. Vrtílek,
Astonomical and Laboratory Detection of the SiC Radical
Astrophys. J. 341, L25–L28 (1989).
The molecule occurs further away from the star than SiS or SiC2 as judged by the line shape. The excitation is probably far from LTE as the transitions within each fine structure component indicate a rotational temperature of around 13 K. In contrast, the relative intensities of the fine structure transitions suggest a temperature closer to 90 K.


Contributor(s): H. S. P. Müller; 09, 2012