FTIR AND DFT STUDY OF THE VIBRATIONAL SPECTRUM OF SiC$_{5}$ TRAPPED IN SOLID Ar

Abstract

This paper follows preliminary results on the SiC$_{5}$ molecule presented earlier. An absorption at 936.9 $\pm$ 0.2 cm$^{-1}$ has been identified as the $\nu_{4}(\sigma)$ Si-C stretching fundamental of linear SiC$_{5}$. Its assignment has been confirmed by the close agreement between DFT predicted and observed $^{13}$C isotopic shifts. DFT-B3LYP calculations predict that two other C-C fundamentals, $\nu_{1}(\sigma)$ and $\nu_{2}(\sigma)$ of SiC$_{5}$ should have intensities 10 to 15 times stronger than $\nu_{4}(\sigma)$, but would appear in the C-C stretching frequency regions. Refinements of the Si-C laser ablation techniques have helped to reveal the isotopic $^{13}$C shifts for two additional absorptions at 2045.0 and 1992.9 cm$^{-1}$. Comparison of their observed isotopic shifts with the predictions of DFT calculations at the MPW1PW91/6-311+G(3fd) level have led to their assignment to the $\nu_{1}(\sigma)$ and $\nu_{2}(\sigma)$ fundamentals of SiC$_{5}$.