Microwave Spectrum, Structure, Dipole Moment, and Internal Rotation of Trimethyl Silane

Abstract

The microwave spectra of eleven isotopic species of trimethyl silane have been measured and assigned. From the observed ground state rotational constants the structural parameters of trimethyl silane are calculated to be $$\begin{array}{cc}\mathrm{CH}\text{\hspace{0.17em}\hspace{0.17em}1.095\hspace{0.17em}}\mathrm{A}& \mathrm{SiH}\text{\hspace{0.17em}\hspace{0.17em}1.489\hspace{0.17em}}\mathrm{A}\\ \mathrm{HCH}{\text{\hspace{0.17em}107}}^{\circ }{56}^{\prime }& \mathrm{SiC}\text{\hspace{0.17em}\hspace{0.17em}1.868\hspace{0.17em}}\mathrm{A}\\ & \mathrm{CSiC}{\text{\hspace{0.17em}110}}^{\circ }{10}^{\prime }\end{array}$$ The equilibrium conformation is found to be the one in which each methyl group staggers the SiH and adjacent SiC bond axes. Stark effect measurements yield a dipole moment of 0.525 debye. Relative intensities of torsional satellites of (CD₃)₂CH₃SiH have been measured and analyzed to provide information about the barrier to internal rotation in trimethyl silane. Structural changes which accompany methylation and fluorination of methyl silane are discussed.