The reactions of Si atoms with NH3 molecules have been studied using matrix-isolation FTIR spectroscopy and density functional theoretical calculations. Silicon atoms reacted with NH3 to form the SiNH3 complex spontaneously in solid argon upon annealing. Mercury arc photolysis with a 290-nm long-wavelength pass filter destroyed the SiNH3 absorptions and produced HSiNH2 absorptions. Full-arc irradiation 250-580 nm) destroyed the HSiNH2 absorptions and produced SiNH absorptions. The potential energy surface along the reaction path leading to the observed products has also been calculated. Similar experiments with Ge gave spectra for the analogous product molecules.