Adsorption, binding, and diffusion of CO2 molecules on model rutile TiO2(110)-1x1 surfaces were investigated experimentally using scanning tunnelling microscopy, infrared reflection adsorption spectroscopy, molecular beam scattering, and temperature programmed desorption and theoretically via dispersion corrected density functional theory and ab initio molecular dynamics. In accord with previous studies, bridging oxygen (Ob) vacancies (VO) were found to be the most stable binding sites. Additional CO2 adsorbs on 5-coordinated Ti sites (Ti5c) with the initial small fraction stabilized by CO2 adsorbed on VO sites. The Ti5c-bound CO2 was found to be highly mobile at 50K at coverages of up to 1/2ML. Theoretical studies showed that the CO2 diffusion on Ti5c rows proceeded via a rotation-tumbling mechanism with the extremely low barrier of 0.06eV. The Ti5c-bound CO2 molecules were found to bind preferentially to a single Ti5c with the O-C-O axis tilted away from the surface normal. The binding energy of tilted CO2 molecules changes only slightly with changes in the azimuth of the CO2 tilt angle. At 2/3ML, CO2 diffusion was hindered and at 1ML an ordered (2x2) overlayer with a zig-zag arrangement of tilted CO2 molecules developed along the Ti5c rows. An out-of-phase arrangement of the zigzag chains was observed across the rows. An additional 0.5ML of CO2 could be adsorbed at Ob sites with a binding energy only slightly lower than that on Ti5c sites presumably due to quadrupole-quadrupole interactions with the Ti5c-bound CO2 molecules.

Structure and Dynamics of CO2 on Rutile TiO2(110)-1x1. Lin, X., Yoon, Y., Petrik, N.G., Li, Z., Wang, Z.T., Glezakou, V.A., Kay, B.D., Lyubinetsky, I., Kimmel, G.A., Rousseau, R., Dohnálek, Z.: Journal of Physical Chemistry C, 2012, 116[50], 26322-34