C-6(-) CARBON CLUSTER ANION - AN INFRARED-ABSORPTION AND RESONANCE RAMAN ISOTOPIC STUDY

The Fourier transform infrared and resonance Raman spectra of the C-6( -) carbon cluster anion has been measured in argon matrices, Fundament al symmetric stretching modes have been observed at 2086, 1775, and 63 4 cm(-1), together with the overtone uf a symmetric bending mode at 46 7 cm(?)(-1). The major asymmetric stretching mode lies at 1936.7 cm(-1 ). Theoretical calculations utilizing Hartree-Fock (B3LYP/6-31G), Mul ler-Plesset perturbation (MP2/6-31G), density functional (B3LYP/6-31G ), and quadratic configuration interaction QCISD/6-31G*, including tr iples 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 st ructure, 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, al though not all isotopomeric bands were observed. The combination of re sonance Raman and Fourier transform infrared spectroscopies with theor etical computations is shown to be a powerful approach for the study o f carbon clusters and their anions.