Vibrational Spectroscopy of Small Silicon-Carbides
Silicon-carbides, e.g., SiC, SiC$_2$ , Si$_2$C, c-SiC$_3$ , and SiC$_4$ , have been found in circumstellar envelopes by means of radio-astronomical observations. They are thought as building blocks of interstellar dust grains featuring the characteristic infrared emission at 11.5 μm
in cool evolved carbon-rich giant stars.
Despite their prominent role in astrochemical processes of dust formation the laboratory spectroscopy of silicon-carbides is still in its infancy and rotationally resolved spectra are rather sparse. In view of a new generation of high resolution infrared telescope instruments, e.g., the Echelon-Cross-Echelle Spectrograph (EXES) onboard SOFIA (Observatory for Infrared Astronomy), accurate laboratory data of small silicon-carbides are of high demand.
We present a general technique to produce gas phase molecules of refractory elements in a supersonic jet. 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. Small silicon-carbides are formed in a free jet expansion and are subsequently cooled by adiabatic expansion into a vacuum chamber. Radiation of quantum cascade lasers at wavelengths of 8-11 μm are used to record rotationally resolved spectra of small silicon-carbide molecules. The high resolution spectra give insights to their molecular structure, the ro-vibrational dynamics and characteristic spectral features for future astrophysical detections.