Using the technique of single vibronic level emission spectroscopy, the ground state vibrational manifolds of jet-cooled HSiF and DSiF have been studied. The radicals were produced in a pulsed electric discharge jet using trifluorosilane (HSiF3 or DSiF3) as the precursor. The gas phase ground state harmonic vibrational frequencies of both isotopomers have been determined for the first time. A normal coordinate analysis using the vibrational frequencies and literature values for the centrifugal distortion constants allowed the determination of all six ground state force constants. Our previous ground state rotational constants have been combined with the calculated harmonic contributions to the alpha constants to obtain an average (r(z)) structure and an estimate of the equilibrium (r(e)(z)) structure. The reliability of the force constants has been evaluated by Franck-Condon simulations of the emission spectra and comparisons of the calculated and experimentally determined inertial defects.