The carbon cluster anions C-5(-), C-7(-), and C-9(-) have been formed via a dual laser beam technique, trapped in Ar matrixes, and studied by infrared spectroscopy. C-13-Isotopic substitution combined with density functional (B3LYP/6-31G*) calculations of vibrational frequencies and intensities has led to the assignment of asymmetric stretching modes in the three anionic clusters. From the excellent fit of the calculated and experimental singly C-13-substituted cluster bands, a linear geometry for all three clusters has been determined.