Raman spectra of selectively deuterated tetramethylammonium ions - I. Methyl deformation vibrations

Article abstract of DOI:10.1016/0584-8539(82)80161-X

The methyl deformation vibrations that have been observed in the Raman spectra of six partially deuterated tetramethylammonium ions are analysed.Strikingly different depolarization ratios were found for the symmetric methyl bending vibration δ_s of a single CH3 group in the Me4N⁺-D₉ ion and the single CD3 group of the Me4N⁺-d₃ species.This observation enables us to explain with some group theoretical considerations a rather puzzling fact, namely that the in-phase symetric CH3 bending vibration ν₂ (A₁) cannot be detected in the Raman spectrum of (CH3)4N⁺, whereas it appears as a rather intense polarized band in the spectrum of the perdeuterated species (CD3)4N⁺.The extent, to which the bending vibrations of neighbouring methyl groups are coupled within the Me4N⁺ ion, is discussed briefly.