Understanding surface photochemistry from first principles: The case of CO–TiO2(1 1 0)

First results concerning laser-induced photodesorption of CO molecules from a TiO2(1 1 0) surface are presented. For the laser-driven process an internal 5σ → 2π∗-excitation within the CO molecule is assumed. In the ground state, electrostatic forces dominate the interaction between the adsorbate and the surface. In contrast, in the excited state, the CO molecule rotates by 180° forming a covalent bond with the oxygen atom pointing downwards to the surface. Subsequent quantum dynamical simulations based on two-dimensional ab initio potential energy surfaces revealed a novel desorption mechanism, which is traced back to unusual interplay of electronic ground and excited state, respectively.