DETECTION OF CYCLIC CARBON CLUSTERS .2. ISOTOPIC STUDY OF THE NU(12)(E(U)) MODE OF CYCLIC C-8 IN SOLID AR

The cyclic C-8 cluster was detected and identified for the first time in Fourier transform infrared spectra of the products from the laser e vaporation of C-13/C-12 rods trapped in Ar at similar to 10 K. Measure ments on spectra produced using both C-12- and C-13-enriched rods comb ined with ab initio predictions have resulted in the assignment of the most intense infrared active mode, nu(12)(e(u)) = 1844.2 cm(-1) of th e cyclic C-8 isomer with C-4h symmetry. A new isotopic perturbation mo del (IPM) in which normal mode information from ab initio calculations is combined with experimental vibrational frequencies was developed i n order to investigate the isotopic vibrational spectrum that is compl icated by the fact that the mode is doubly degenerate and mixes with t wo infrared inactive modes lying nearby. The assignment of nu(12)(e(u) ) is based on excellent agreement of the frequency, C-13 isotopic shif ts, and relative intensities with the predictions of earlier density f unctional theory (DFT) calculations and perturbation treated DFT/B3LYP /cc-pVTZ calculations using the IPM model carried out in the present s tudy. (C) 1997 American Institute of Physics.