Fourier transform infrared matrix measurements carried out in conjunction with ab initio calculations reported in a companion paper by Rittby have resulted in the first identification of two fundamental vibrations, the C=C stretching mode nu3(sigma(u))=1955.2 cm-1, and the Si-C stretching mode nu4(sigma(u))=898.9 cm-1 of the SiC3Si cluster formed by trapping the products of the vaporization of silicon/carbon mixtures in Ar at 10 K. The observed frequencies, relative intensities, and C-13, Si-29, and Si-30 isotopic shifts for the nu3 and nu4 vibrations are in good agreement with the results of the ab initio calculations at the second-order many-body perturbation theory [MBPT(2)] level which predict a linear centrosymmetric geometry for the ground state Of SiC3Si. The results of force constant adjustment calculations are consistent with the proposed vibrational assignments and structure.