Spectroscopic characterization of novel hydrogen-bearing silicon-carbon clusters

Abstract

Fourier transform infrared studies of hydrogen-bearing silicon-carbon clusters produced by vacuum ultraviolet (VUV) photolysis and trapped in Ar matrices have resulted in the first identification of the SiCCH, H$\sb2$SiCCH and SiCH clusters. The vibrational spectrum of linear SiCCH was produced by trapping the products of the vacuum ultraviolet photolysis of a mixture of SiH$\sb4$ silane, and $\rm C\sb2H\sb2$ acetylene, in an Ar matrix at $\sim$10 K. Assignments of two vibrational fundamentals are proposed, the $\nu\sb2(\sigma)$ C-C stretching mode at 1989.8 cm$\sp{-1}$ and $\nu\sb3(\sigma)$ Si-C stretching mode at 636.0 cm$\sp{-1}.$ Comparison of extensive measurements of isotopic shifts resulting from $\sp{13}$C and deuterium substitutions with the results of new ab initio calculations at the CCSD(T) level with a 6-311G** basis set, which were performed in conjunction with the present experimental work, strongly support the assignment of the $\nu\sb2$ mode. However, a discrepancy between the observed and predicted deuterium shifts for the proposed $\nu\sb3$ mode of SiC$\sb2$H make its assignment less certain. A Fourier transform infrared study has resulted in the first observation of a vibrational spectrum of the non-planar H$\sb2$SiCCH. Two vibrational fundamentals have been observed, the $\nu\sb3(a\sp\prime),$ silicon-carbon stretching mode at 2055.6 cm$\sp{-1}$ and the $\nu\sb4(a\sp\prime),$ hydrogen-silicon bending mode at 926.8 cm$\sp{-1}.$ The vibrational frequencies, relative intensities, and extensive measurements of D and $\sp{13}$C isotopic shifts are all in good agreement with the values predicted by new density functional theory calculations at DFT B3LYP/cc-pVDZ level. Linear SiCH was produced by vacuum ultraviolet (VUV) photolysis of a mixture of silane (SiH$\sb4)$, and methane (CH$\sb4),$ trapped in an Ar matrix at 10 K, and the $\nu\sb1(\sigma),$ silicon-carbon stretching mode has been observed for the first time at 1010.4 cm$\sp{-1}.$ The results of extensive measurements of D and $\sp{13}$C isotopic shifts are in good agreement with the results of new ab initio calculations performed at the CCSD(T)/6-31G** (coupled cluster with single, double and triple excitations) level, and confirm the identification. The observation of these hydrogen-bearing silicon-carbon clusters provides valuable spectroscopic information on their structures, serves as an important guide for gas phase study and astrophysical detection, and helps in analyzing and controlling chemical reactions in industrial applications.