2020A&A...637A..81Z

Small silicon-carbon clusters are important gas-phase constituents of stellar atmospheres, and are thought to play a role as potential seeds of the interstellar dusts formed in the envelopes of evolved carbon stars. Here we present the high-resolution optical spectra of the linear SiC₂Si molecule (l-Si₂C₂) studied via laboratory experiments. The l-Si₂C₂ molecules are generated in a supersonically expanding planar plasma by discharging a silane-acetylene-argon gas mixture. The optical absorption spectra in the 5000-5300 Å region are recorded using sensitive pulsed cavity ring-down spectroscopy. In total, five optical absorption bands belonging to the C∼³Σi^–_u–X∼³Σ^–_g electronic transition system of l-Si₂C₂ are measured with fully resolved spin splitting fine structures in individual rotational transitions. Accurate spectroscopic constants for both X∼³Σ^–_g and C∼³Σ^–_u states of l-Si₂C₂, including the spin-spin interaction constants and spin-rotation interaction constants, are determined from the experimental spectra, which can be used to simulate these optical bands with different temperatures. Using the determined spectroscopic constants, optical spectra of l-Si₂C₂ simulated with different rotational excitation temperatures are compared to the stellar spectra of evolved carbon stars V Hya and IRAS 12311-23509, where the triatomic SiC₂ are known to be abundant. Tentative assignments of the l-Si₂C₂ spectral features in the stellar spectra are discussed.