molecules:ism:sic_2n_1 [CDMS classic documentation]

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===== On SiC<sub>2n+1</sub> (n ≥ 1) Radicals around CW Leonis =====

J. Cernicharo, J. R. Pardo, M. Agúndez, J. P. Fonfría, L. Velilla-Prieto, C. Cabezas, B. Tercero, P. de Vicente and M. Guélin \\
announced\\
**[[https://doi.org/10.1051/0004-6361/202556370|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 <sup>3</sup>Σ<sup>−</sup> 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 (SiC<sub>3</sub>), all three strong fine structure (FS) components with Δ//J// = Δ//N// 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 (SiC<sub>5</sub>), 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//<sub>rot</sub> were estimated as ~5 and ~17 K for SiC<sub>3</sub> and SiC<sub>5</sub>, respectively. The abundance ratios of the prolate rhomboidal (bicyclic) SiC<sub>3</sub> to the linear forms of SiC<sub>3</sub> and SiC<sub>5</sub> are roughly 4 : 2 : 1. Similar values are obtained if instead of rhomboidal SiC<sub>3</sub> (linear) SiC<sub>4</sub> is taken.\\
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Contributor(s): H. S. P. Müller; 09, 2025

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