FT-IR spectroscopic studies of the adsorption of natural and O-18-enriched NO gases on thermally and cleaned MgO powders were carried out. The temperature dependence of the IR spectra was investigated to characterize the adsorbate species. Three types [1, 2, and 3] of NO adsorptions were obtained in the wavenumber region of 1500-1000 cm(-1). Those types were examined using density functional theory [(U)B3-LYP/6-31G*] vibrational analyses of (MgO)(n)-NO cluster calculations. Types 1, 2, and 3 were assigned to monodentate, asymmetric, and symmetric bidentate geometries, respectively. A type 4, a "tridentate" model which involves a NO3-like species, was calculated and was found to give wavenumbers of less than 1000 cm(-1). The splitting of IR bands of type 3 due to the (NO)-N-15-O-18 adsorbate was ascribed to the oxygen exchange, (NO)-N-15-O-18 --> (NO)-N-15-O-16, via the reaction O-16-N-15-O-18 --> O-16 -->N-15-O-16 on MgO surfaces.