The reactions of N-phenylphthalimide films with ozone have been studied under a variety of conditions : dry ozone, moist ozone, ozone plus ultraviolet light, as well as ozone plus water vapor plus ultraviolet light. This compound is a conveniently available model for imide polymers. These reaction conditions represent simulation of certain aspects of the space environment. For each set of reaction conditions the reaction products were determined by combined gas chromatography/mass spectrometry. Semiempirical molecular orbital computations were made of the relative energetics of possible reaction pathways consistent with the generation of the observed products. The reaction products found indicate fragmentation of the imidic moiety for which the energetics are favorable.