INFRARED-SPECTROSCOPY OF MATRIX-ISOLATED CARBON CLUSTERS, WITH EMPHASIS ON C-8 AND C-9

Infrared spectra of neutral linear all-carbon clusters, produced by la ser ablation of graphite, have been investigated in Ne, Ar and Kr matr ices. The effects of thermal annealing on the infrared intensities hav e been used together with results from recent high level ab initio and density functional theory (DFT) calculations to locate several hereto fore unknown infrared bands of linear C-8 and C-9 clusters. Specifical ly, two infrared bands located at 2071.5 cm(-1) and 1710.5 cm(-1) (Ar matrix), are shown to be well correlated and to match closely the dens ity functional theory (DFT) predictions of 2109 cm(-1) (1366.3 km/mol) and 1703 cm(-1) (984.8 km/mol) by Hutter, Luthi and Diederich (HLD) f or the linear C-8 cluster. A moderately intense band has also been loc ated at 2078 cm(-1) (Ar matrix) and is shown to correlate well with th e two known C-9 bands at 1601 cm(-1) and 1998 cm(-1). This band is als o shown to match well with the DFT predictions of HLD and is assigned to the nu(5) mode of linear C-9. Combination bands involving symmetric and asymmetric stretching modes have been observed for C-5, C-6, C-7 and C-9 and are used to estimate the totally symmetric frequencies for thesez species. Good agreement with theory is found. Finally, anharmo nicity constants for the prominent asymmetric stretching frequencies a re determined from the overtone bands of C-3, C-5, C-6, C-7 and C-9.