Microwave Spectrum, Internal Barrier, Structure, Equilibrium Configuration, and Dipole Moment of Methyl Monofluorosilane

Abstract

The microwave spectrum of methyl monofluorosilane has been investigated in the region 18 to 38 kmc. Several transitions of the isotopic species CH3SiH2F and CH3SiD2F are split into doublets because of coupling of internal and over-all rotation. These splittings give a barrier to internal rotation of 1559±30 cal/mole. The form of the potential barrier was assumed to be V=12V3(1−cos3α). A few transitions belonging to the first excited torsional state were observed and assigned. The splittings in the excited state are consistent with the barrier as determined from ground state observations. Rotational constants of CH3SiH2F, CH3SiD2F, C13H3SiH2F, CD3SiH2F, and CH3SiDHF have been determined and were used to calculate the structure of the molecule. The structural parameters are: SiC1.848 ACSiF109∘ 13′SiF1.600HCH107∘ 52′SiH1.473CSiH109∘ 28′ (assumed)CH1.090HSiH109∘ 28′ (assumed). A study of CH2DSiH2F proves conclusively that methyl monofluorosilane in its equilibrium configuration has the methyl group staggered with respect to the SiH2F group. The dipole moment was found to be 1.71D.