Infrared Spectroscopy of Disilicon-Carbide, Si₂C: The ν₃ Fundamental Band

The ν₃ antisymmetric stretching mode of disilicon-carbide, Si₂C, was studied using a narrow line width infrared quantum cascade laser spectrometer operating at 8.3 μm. The Si₂C molecules were produced in an Nd:YAG laser ablation source from a pure silicon sample with the addition of a few percent methane diluted in a helium buffer gas. Subsequent adiabatic expansion was used to cool the gas down to rotational temperatures of a few tens of kelvin. A total of 183 infrared transitions recorded in the spectral range between 1200 and 1220 cm^-1 were assigned to the fundamental ν₃ mode of Si₂C. In addition, pure rotational transitions of K_a = 1 and 2 between 278 and 375 GHz were recorded using a supersonic jet spectrometer for submillimeter wavelengths. Molecular parameters for the ( v₁ v₂ v₃) = (001) vibrationally excited state were derived and improved molecular parameters for the vibrational ground-state (000) were obtained from a global fit data analysis, which includes our new laboratory data and millimeter wavelength data from the literature. We found the rotational levels K_a = 0 and K_a = 2 in the vibrationally excited (001) state being perturbed by a Coriolis-type interaction with energetically close lying levels of the symmetric stretching and triple-excited bending mode (130). The data analysis was supported by quantum chemical calculations performed at the coupled-cluster level of theory. All experimental results were found to be in excellent agreement with the theory.