AVS 60th International Symposium and Exhibition
    Surface Science Thursday Sessions
       Session SS+EN-ThM

Paper SS+EN-ThM5
Energy Transfer and Photostimulated Desorption of Atoms and Molecules Co-adsorbed with Oxygen on TiO2(110) Surface

Thursday, October 31, 2013, 9:20 am, Room 201 A

Session: Photocatalysis and Photochemistry at Surfaces
Presenter: N.G. Petrik, Pacific Northwest National Laboratory
Authors: N.G. Petrik, Pacific Northwest National Laboratory
G.A. Kimmel, Pacific Northwest National Laboratory
Correspondent: Click to Email
Titanium dioxide is a widely used photocatalyst. However, fundamental aspects of the photochemistry, including the role of molecular oxygen in photooxidation reactions, are still actively debated. Here, we use weakly bound (i.e. physisorbed) atoms and molecules, such as Ar, Kr, Xe, CO2 and N2, to probe the photochemical interactions of O2 on rutile TiO2(110). UV irradiation of chemisorbed O2 along with the physisorbed probe species lead to photon-stimulated desorption (PSD) of the probe species. Without O2, the PSD yields of the probe species are very low or not observable. However, the Ar, Kr and N2 PSD yields increase with increasing coverage of chemisorbed O2. No PSD was observed for CO2, and the PSD yield for Xe is very low compared to the other probe atoms or molecules. The angular distribution of the photo-desorbing Kr, which is broad and cosine, is quite different from the O2 PSD angular distribution, which is sharply peaked along the surface normal. We propose a mechanism for the observed phenomena, where the chemisorbed O2 serve as photoactive centers, excited via electronic excitations (electrons and/or holes) created in the TiO2 substrate by UV photon irradiation. The photo-excited O2 may transfer its energy to neighboring co-adsorbed atoms or molecule resulting in their desorption. Simple momentum transfer considerations suggest that heavier adsorbates (like Xe) and adsorbates with higher binding energy (like CO2) would desorb less efficiently according to the proposed mechanism.