J. Cernicharo, J. R. Pardo, M. Agúndez, J. P. Fonfría, L. Velilla-Prieto, C. Cabezas, B. Tercero, P. de Vicente and M. Guélin
announced
Detection of the linear SiC3 and SiC5 radicals in IRC+10216
Astron. Astrophys. 700, Art. No. L20 (2025).
Propadienediylidenesilylene and pentatetraenediylidenesilylene, which are also known as silatetratrienediylidene and silahexapentaenediylidene, respectively, were detercted in their ³Σ⁻ ground electronic states in the envelopes of the prototypical carbon-rich late-type AGB star CW Leonis in the course of a molecular line survey in the 31.0 to 50.3 GHz region carried out with the 40 m Yebes telescope. In the case of propadienediylidenesilylene (SiC₃), all three strong fine structure (FS) components with ΔJ = ΔN of the four transitions with 5 ≤ N ≤ 9 were covered. Two FS components were heavily blended, the other ones unblended or partially blended, though the ones pertaining to the highest N have a rather modest signal-to-noise ratio. In the case of pentatetraenediylidenesilylene (SiC₅), FS components of transitions with 16 ≤ N ≤ 25 were covered. While several of them are severely blended, sufficiently many are unblended or partially blended. The values of T_rot were estimated as ~5 and ~17 K for SiC₃ and SiC₅, respectively. The abundance ratios of the prolate rhomboidal (bicyclic) SiC₃ to the linear forms of SiC₃ and SiC₅ are roughly 4 : 2 : 1. Similar values are obtained if instead of rhomboidal SiC₃ (linear) SiC₄ is taken.

Contributor(s): H. S. P. Müller; 09, 2025