The geometry and vibrational spectrum of the previously not studied silicon-carbon cluster Si2C3 has been investigated. Geometries and frequencies for a number of isomeric structures are presented at the Hartree-Fock level. In agreement with a concurrent experimental observation the ground state is found to be linear. Harmonic frequencies, isotopic shifts, and infrared intensities calculated using many-body perturbation theory to second order are found to be in good agreement with the experimental results supporting the identification of a new penta-atomic silicon-carbon cluster. The general behavior of penta-atomic silicon-carbon clusters is discussed and preliminary ground state geometries and harmonic frequencies are presented for Si3C2 and Si4C.