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: vertical bar mu(a)vertical bar = 1.041(5), vertical bar mu(b)vertical bar = 1.311(6), and vertical bar mu(t)vertical bar = 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r(0)) in Angstroms are: Si-C = 1.8942(57) and C-F = 1.4035(55) and the angle in degree, angle SiCF = 109.58(14). A semi-experimental r(e) 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 bands at 138.8 and 127.5 cm(-1). The barrier to internal rotation was obtained as 717.3(16) cm(-1) (2.051(46) kcal mol(-1)) by combining the analysis of the microwave A and E splittings and the torsional fundamental and hot band frequencies. Ab initio calculations have been carried out with full electron correlation by the second-order perturbations method with several different basis sets up to MP2/6-311+G(d,p) to obtain geometrical parameters, barriers to internal rotation, and centrifugal distortion constants. Adjusted r(0) structural have been obtained by combining b initio MP2/6-311+G(d,p) predicted values With the determined rotational Constants for the fluoride as Well as With the previously reported microwave data for the chloro- and bromo- compounds. These experimental results are compared to the corresponding parameters for the carbon analogues.