Abstract Unlike dark catalytic reactions, mainly dependent on the last-layer atomic arrangement, photoreactions on semiconductor surfaces depend necessarily on the bulk properties of the solid materials. Decoupling of the effect of surface and bulk structures can be obtained by allowing for surface reconstruction. The photocatalytic reaction of acetic acid on the two different reconstructed surfaces of TiO 2 (001) single crystal (the {011}- and the {114}-faceted surfaces) under ultrahigh vacuum conditions was conducted. The reaction products (ethane, methane, water and CO 2 : photo-Kolbe reaction) were found to be similar on both reconstructed surfaces. Quantitative analyses show, however, a large difference in reactivity. The low temperature annealed surface, the {011}-faceted surface, was found far more reactive than the high temperature annealed surface, the {114}-faceted surface. The quantum yield of the reaction of acetic acid was found equal to 0.05 and 0.02 for the {011}- and {114}-faceted surfaces, respectively. This large difference in reactivity is solely due to the collective changes of the electric field created by changing the last-layer atomic arrangement. From the catalytic reaction, the depletion layer width ( W ) and barrier height ( V ) for both surfaces could be computed. The depletion layer widths ( as well as the barrier heights ) were found equal to 18.2 and 6.6 nm (0.18 and 0.023 V) for the {011}- and {114}-faceted surfaces, respectively.