The ArF excimer laser induced photochemistry of silane-ammonia mixtures has been studied with molecular beam sampling mass spectrometry. The observed products include disilane, trisilane, and all possible aminosilanes, SiHx(NH2)4-x, x = 0-3. These products are formed under steady-state photolysis conditions and under single-laser-pulse conditions. A mechanism for the formation of these species is proposed and quantitatively evaluated. © 1990 American Chemical Society.