Low temperature Raman study of bis(trimethylsilyl)acetylene

Low temperature Raman spectroscopy was applied in study of bis(trimethylsilyl)acetylene (BTMSA), a known catalyst with very low barrier for the internal rotation of methyl groups – less than 10 cal/mol (Sipachev et al. J. Mol. Struct. 523 (2000) 1). Since crystals consisting of flexible molecules often show polymorphism, it was of interest to find out if it is the case of BTMSA.Phonon Raman spectra recorded from 10 to 323 K were in complete agreement with previously determined crystal structure: for space group P21/c with Z = 2 six phonons are expected and six are observed below 100 cm−1. BTMSA crystallizes in trans confromation, also the most stable one in gas phase. All observed bands could be attributed to crystal splitting of molecular g modes of D3d symmetry into Ag and Bg modes of the point group C2h of the crystal.