We report the first detection of SiC2 in the interstellar medium. The molecule was identified through six rotational transitions toward G\,+0.693−0.027, a molecular cloud located in the Galactic center. The detection is based on a line survey carried out with the GBT, the Yebes 40m, and the IRAM 30m telescopes covering a range of frequencies from 12 to 276 GHz. We fit the observed spectra assuming local thermodynamic equilibrium and derive a column density of (1.02±0.04)×1013 cm−2, which gives a fractional abundance of 7.5×10−11 with respect to H2, and an excitation temperature of 5.9±0.2 K. We conclude that SiC2 can be formed in the shocked gas by a reaction between the sputtered atomic silicon and C2H2, or it can be released directly from the dust grains due to disruption. We also search for other Si-bearing molecules and detect eight rotational transitions of SiS and four transitions of Si18O. The derived fractional abundances are 3.9×10−10 and 2.1×10−11, respectively. All Si-bearing species toward G\,+0.693−0.027 show fractional abundances well below what is typically found in late-type evolved stars.
@article{arxiv.2308.09459,
title = {The first detection of SiC$_2$ in the interstellar medium},
author = {S. Massalkhi and I. Jiménez-Serra and J. Martín-Pintado and V. M. Rivilla and L. Colzi and S. Zeng and S. Martín and B. Tercero and P. de Vicente and M. A. Requena-Torres},
journal= {arXiv preprint arXiv:2308.09459},
year = {2023}
}