Infrared and Raman Spectra of Tetramethylmethane-d12

Abstract

In order to study further the molecular vibrations of tetramethylmethane and of hydrocarbons in general, tetramethylmethane‐d₁₂ was synthesized, and its Raman and infrared absorption spectra were obtained. The missing nondegenerate mode, ν₂(a₁), in ordinary tetramethylmethane was predicted by the Teller‐Redlich product rule to lie at about 1430 cm⁻¹ where it would be obscured by a strong depolarized Raman band at 1451 cm⁻¹. A unique narrowness in the 1200 cm⁻¹ infrared absorption bands of tetramethylmethane and tetramethylmethane‐d₁₂ and double maxima of small separation in the band of tetramethylmethane resulted in assigning these frequencies to methyl wagging modes of unsymmetrical character. The over‐all results of this investigation cast doubt on the validity of extending theoretical considerations of tetrahedral XY₄ systems to the tetrahedral tetramethyl molecules with the assumption of the methyl groups as point masses.