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A Fourier transform study of the vibrational spectrum of Si,C produced by quenching the products of the vaporization of carbon/silicon mixtures in Ar at 13 K has confirmed a previously observed band at $1180.4cm-1$ as the antisymmetric 5i--C streching mode, and led to the identification of a new vibration at $839.5cm-1$ as the symmetric Si-Si streching mode. The bending mode was not observed. These results are confirmed by $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}Cr$, $\mathrm{<mrow\; data-mjx-texclass="ORD">19</mrow>}Sir$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">30</mrow>}Si$ isotopic data and are in excellent agreement with the predictions of second order perturbation theory [MBPT2/6-311G(2d)] calculations carried out in conjunction with this work. Force constant adjustment calculations based on these assignments confirm the ground state geometry as a floppy bent symmetrical structure.