The Fourier transform infrared and resonance Raman spectra of the C-6(-) carbon cluster anion has been measured in argon matrices, Fundamental symmetric stretching modes have been observed at 2086, 1775, and 634 cm(-1), together with the overtone uf a symmetric bending mode at 467 cm(?)(-1). The major asymmetric stretching mode lies at 1936.7 cm(-1). Theoretical calculations utilizing Hartree-Fock (B3LYP/6-31G*), Muller-Plesset perturbation (MP2/6-31G*), density functional (B3LYP/6-31G*), and quadratic configuration interaction QCISD/6-31G*, including triples QCISD(T)/6-31G*, support the assignment of these bands to the C-6(-) cluster and indicate that it is linear with an acetylenic-like structure, Frequency shifts determined from infrared and resonance Raman studies of C-12/C-13 isotopically substituted C-6(-) are generally in excellent agreement with the calculated isotopic frequency shifts, although not all isotopomeric bands were observed. The combination of resonance Raman and Fourier transform infrared spectroscopies with theoretical computations is shown to be a powerful approach for the study of carbon clusters and their anions.