O-18-Selective-infrared multiple photon decomposition of diisopropyl ether has been studied in detail using samples with O-18 at oxygen atomic fractions of 0.20% (natural abundance ratio), 4.5%, and 17.3%. The 1022 cm(-1) band due to the C-12-O-16-C-12 antisymmetric stretching vibration was found to shift toward a low-energy side by 24 cm(-1) for C-12-O-18-C-12. The O-18-selectivities and yields of the main products containing oxygen, acetaldehyde, and 2-propanol were examined as functions of experimental parameters. The irradiation of a few Torr (1 Torr = 1 mmHg = 133.322 Pa) of diisopropyl ether with TEA (transversely excited atmospheric) CO2 laser lines in the vicinity of 950 cm(-1) resulted inconsiderably high enrichment of O-18 in the products. The fluence at focus was more or less than 8 J cm(-2). Acetaldehyde and 2-propanol containing O-18 at about 20% were obtained from natural ether, and those containing more than 70% were obtained from 17.3% O-18-enriched ether. The observed results;can be explained in term of the mechanism involving radical and; molecular decomposition channels.