Microwave Spectrum, r0 Structure, Dipole Moment, Barrier to Internal Rotation, and Ab Initio Calculations for Fluoromethylsilane

The microwave spectra of seven isotopomers of fluoromethylsilane, CH2FSiH3, in the ground vibrational state were measured and analyzed in the frequency range 18−40 GHz. The rotational and centrifugal distortion constants were evaluated by the least-squares treatment of the observed frequencies of a- and b-type R- and b-type Q-transitions. The values for the components of the dipole moment were obtained from the measurements of Stark effects from both a- and b-type transitions and the determined values are: |μa| = 1.041(5), |μb| = 1.311(6), and |μt| = 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r0) in Angstroms are: Si−C = 1.8942(57) and C−F = 1.4035(55) and the angle in degree, ∠SiCF = 109.58(14). A semi-experimental re structure was also determined from experimental ground state rotational constants and vibration−rotation constants derived from ab initio force fields. The internal torsional fundamental, SiH3, was observed at 149.2 cm−1 with two accompanying hot ba...