INFRARED SPECTROSCOPY OF DISILICON-CARBIDE, Si2C

Abstract

Small silicon and carbon containing molecules are thought to be important building blocks of interstellar grains. Some of them have been detected in circumstellar environments of late-type stars by means of rotational spectroscopy e.g., SiC, SiC$_2$, Si$_2$C, c-SiC$_3$, SiC$_4$, while centro-symmetric species, e.g., C$_3$, C$_4$, C$_5$, Si$_2$C$_2$, Si$_2$C$_3$, can only be detected by vibrational transitions, mainly in the infrared. _x000d_ In view of a new generation of high resolution infrared telescope instruments, e.g., EXES (Echelon-Cross-Echelle Spectrograph) onboard SOFIA (Observatory for Infrared Astronomy) and TEXES (Texas Echelon Cross Echelle Spectrograph) at the Gemini-North observatory, accurate laboratory data of small silicon-carbides in the infrared region are of high demand. In this talk we present first laboratory data of the Si$_2$C asymmetric stretching mode at 1200 cm$^{-1}$. A pulsed Nd:YAG-laser is used to vaporize a solid target of silicon exposed to a dilute sample of methane in helium buffer gas. Si$_2$C is formed in an adiabatic expansion of a supersonic jet and radiation of a quantum cascade laser is used to record rotationally resolved spectra. To date, 160 ro-vibrational lines and have been assigned to the asymmetric stretching vibration of Si$_2$C, and derived molecular parameters are in excellent agreement with ab initio calculations. In our global fit analysis recently published microwave laboratory data (McCarthy {it et al.} 2015)footnote{McCarthy M.C., Baraban J.H., Changala P.B., Stanton J.F., Martin-Drumel M.A, Thorwirth S., et al., {it J. Chem. Phys. Lett.} {bf6}, 2107–2111 (2015).} and astronomical data (Cernicharo {it et al.} 2015)footnote{Cernicharo J., McCarthy M.C., Gottlieb C.A., Agundez M., Velilla Prieto L., Baraban J.H., et al. {it Astrophys. J. Lett.} {bf 806},L3 (2015).} were taken into account. Our new results allow for the identification of Si$_2$C by means of high resolution infrared astronomy towards the warm background of carbon-rich stars._x000d_ _x000d_ _x000d_ _x000d_ _x000d_