We have conducted a series of temperature programmed desorption (TPD) experiments to study the photoinduced reactions of methanol (CH3OH) on a rutile(R)TiO2(110) surface with 355 nm light. Products formaldehyde (CH2O) and water (H2O) have been detected. The results clearly show that the photochemistry of CH3OHTisc is hindered by the coadsorbed multilayer CH3OH or H2O. For multilayer CH3OH adsorption, CH3OH molecules hydrogen-bonded to the bridge bonded oxygen sites inhibit the CH3OHTisc photochemistry. Combined with previous theoretical studies (Sci. China Chem. 2015, 58, 614-619), CH3OH molecules hydrogen bonded to the BBO sites increase the energy barrier of C-H bond dissociation and decrease the energy barrier of the reverse reaction, resulting in lowering the efficiency of CH3OHTisc photolysis. As the coverage of CH3OH keeps increasing to multilayer, the efficiency of the CH3OHTisc photolysis does not decrease any more. However, with the coadsorbed H2O molecules, the efficiency of CH3OHTi5c photolysis decreases continually with increasing H2O coverage, which is likely due to the decrease of the, chemisorbed CH3OHTisc molecules via molecule exchange between the H2O films and the chemisorbed CH3OH layer that occurs at similar to 100 K and the complicated hydrogen bonds formed between H2O and CH3OHTisc molecules
