Thin crystalline films of Al2O3 have been grown by reaction of a NiAl(111) surface with chemisorbed O at elevated temperature. The resulting Al2O3/NiAl buried metal layer structure has then been used as a substrate for studies of NH3 adsorption under steady-state conditions at similar to 300 K and up to similar to 200 Torr. The technique used is polarization-modulated infrared reflection absorption spectroscopy, the application of which to in situ studies of surface chemistry is described in detail : Evidence is seen that suggests incorporation of N into the Al2O3, and adsorbed NH3 is detected under high (greater than or equal to 25 Torr) static pressures. [S0734-2101(98)07604-0].