VIBRATIONAL SPECTROSCOPY OF SMALL MATRIX-ISOLATED LINEAR CARBON CLUSTER ANIONS

Carbon cluster anions have been generated, deposited in an argon matri x, and studied spectroscopically. A new method involving a dual laser beam-induced Ar plasma using Y or W metal and graphite targets is intr oduced for the efficient production of matrix-isolated carbon cluster anions. New bands found in the infrared spectra of the deposited plasm a mixture have been assigned to asymmetric stretching modes of the C-3 , C-5, C-6, C-7, and C-9 anions. Density functional theory calculation s (B3LYP/6-31G level) support the attribution of these bands to linea r carbon cluster anions. Calculational results also indicate that reac tions between linear anionic clusters and linear neutral clusters are highly exothermic and that aggregation between anions and even-membere d neutrals are more highly exothermic than between anions and odd-memb ered neutrals. The anion infrared bands are found to be photosensitive at irradiation wavelengths shorter than a certain threshold value. Th ese values are ca. 0.5 eV higher than the corresponding vertical detac hment energies of the vapor phase C-n(-) species. The possibility that longer chain carbon anions are present in the carbon-rich circumstell ar envelopes of carbon stars is discussed.