Vibrational spectra of tetra-atomic silicon–carbon clusters. I. Rhomboidal Si3C in Ar at 10 K

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Abstract
The vibrational spectrum of Si3C has been observed for the first time in a Fourier transform infrared study of the products of the vaporization of carbon/silicon mixtures trapped in Ar at 13 K. Five of the six fundamental modes have been assigned: the symmetric breathing vibration, ν1(a1)=658.2 cm−1; the Siβ–Siα–Siβ symmetric deformation vibration, ν2(a1)=511.8 cm−1; the Siβ–C–Siβ symmetric deformation vibration, ν3(a1)=309.5 cm−1; the Siβ –C antisymmetric stretching vibration, ν5(b2)=1101.4 cm−1; and the Siα–Siβ antisymmetric stretching vibration, ν6(b2)=357.6 cm−1. The assignments are supported by 13C, 29Si, and 30Si isotopic data and are in excellent agreement with the predictions of an ab initio study carried out by Rittby in collaboration with this work. The results of force constant adjustment calculations are consistent with the ground state geometry established by the ab initio calculation, a rhomboidal structure of C2v symmetry, with carbon–silicon transannular bonding between the two equivalent Siβ atoms.