The reaction of silyl iodide and ammonia has been studied under slowly flowing conditions using FTIR spectroscopy and mass spectroscopy. At low (0.01 mbar) partial pressures of silyl iodide in excess ammonia, monosilylamine, a long postulated intermediate in the synthesis of trisilylamine from halosilanes and ammonia, was the only silylamine observed by mass spectroscopy and infrared spectroscopy. At a silyl iodide pressure of 0.1 mbar (necessary to obtain a high signal-to-noise infrared spectrum of silylamine) a significant amount (∼10%) of disilylamine was observed by both infrared and mass spectroscopies, demonstrating that both monosilylamine and disilylamine intermediates are produced in the gas phase. Trisilylamine was not observed as a product of the gas-phase reaction of silyl iodide and ammonia under the low-pressure conditions studied. By study of the reaction of deuterated silyl iodide and ammonia and the reaction of silyl iodide with deuterated ammonia, it was determined that the hydrogen lost in the formation of hydrogen iodide originates from the ammonia molecule. The infrared spectra of SiH3NH2, SiH3ND2, SiD3NH2, and SiD3ND2 are reported. © 1992, American Chemical Society. All rights reserved.