Fourier transform infrared measurements on the spectra of the products of the vaporization of silicon/carbon mixtures trapped in argon at similar to 10 K combined with the results from a published ab initio study and from new theoretical calculations carried out in the present work, have resulted in the first observation of a spectrum for the pentagonal Si3C2 cluster. Three vibrational fundamentals have been assigned : the v(2)(a(1)) symmetric "breathing" vibration at 681.1 cm(-1), the v(7)(b(2)) Si-alpha-C-C-Si-alpha stretching deformation at 956.7 cm(-1) and the v(8)(b(2)) C-Si-beta-C antisymmetric stretching vibration at 597.8 cm(-1). The observed frequencies, relative intensities, and C-13, Si-29, and Si-30 isotopic shifts are in excellent agreement with the theoretical predictions.