The photooxidation of an organic compound, 2-chloroethyl ethyl sulfide (2-CEES), over a TiO2-SiO2 mixed oxide photocatalyst has been studied using transmission infrared spectroscopy. The purpose of this work was to determine the influence of an inert perfluoroalkane buffer layer on the photooxidation properties of the photocatalyst. Both oxygen gas and 2-CEES were adsorbed on top of a thick C9F20 layer, and it was found that the diffusion of both of the reactants through the solid perfluoroalkane layer occurs readily at 253 K. Adsorption of 2-CEES and 02 therefore occurs at the photocatalyst surface, and photooxidation of the 2-CEES is little impeded by the inert C9F20 layer. Both C9F20 and 2-CEES cause characteristic frequency shifts due to hydrogen bonding with Si-OH groups on the photocatalyst, and this effect may be used spectroscopically to monitor the displacement of hydrogen-bonded C9F20 molecules from the Si-OH groups by the 2-CEES molecule. In addition, IR spectroscopy has been used to monitor the diffusion of oxygen gas through the perfluoroalkane layer, and it has been found that O-2 diffusion occurs at 253 K.