Propylene and O-2 loaded into zeolite BaY were found to react upon irradiation with green or blue light in a single photon process. In situ monitoring by FT-infrared spectroscopy showed that allyl hydroperoxide is the predominant product at -100 degrees C. At room temperature, acrolein, propylene oxide, and allyl hydroperoxide were observed in comparable amounts. The aldehyde and epoxide are shown to emerge from secondary thermal chemistry of the allyl hydroperoxide photoproduct. The selectivity in terms of the hydroperoxide photoproduct is very high (98% at room temperature) even at high propylene conversion. Diffuse reflectance spectra show that access to the mild oxidation path is made possible by a zeolite-induced shift of the propylene . O-2 charge-transfer absorption from the UV into the visible region.