Knowledge Bank

Gas, solid and matrix phase spectra of $(CH3)3N$ and $(SiH3)3N$ have been investigated in the region 4000 to $250cm-1$. Several previous $studies1,2,2$ of the spectrum of $(CH3)3N$ have been reported. None of these investigators gave a complete assignment of the vibrations due to overlapping bands in the gas phase spectrum. The present matrix results yield all of the expected fundamental absorptions assuming $C3v$ symmetry for the molecule. The frequencies observed below $500cm-1$ are $433cm-1,388cm-1,293cm-1$ and $277cm-1$. While the frequencies at $433cm-1,388cm-1$ and $293cm-1$ are assigned to $NC3$ asymmetric deformation $\nu 21(E),NC3$ symmetric deformation $\nu 7(A1)$, and $CH3$ torsional $\nu 22(E)$ vibrations respectively, the frequency at $277cm-1$ can be interpreted only as due to the infrared inactive torsional $\nu 11(A2)$ vibration which has become active as a result of a lowering of symmetry in the solid. The observed fundamental frequencies of $(SiH3)3N$ are in general agreement with the ones previously $observed4,5$ and suggests that the molecule belongs to the point group $C2b$. Neither the $SiH3$ torsional frequency $\nu 18(A\prime \prime )$ nor the $NSi3$ deformation frequencies $\nu 13(E\prime )$ and $\nu 17(A\prime \prime )$ have been observed. They are assumed to lie below $250cm-1$. The special features of the solid spectra including the splitting of the degenerate vibrations will be discussed.