Electronic structure and quantum dynamics of photoinitiated dissociation of O2 on rutile TiO2 nanocluster

Abstract

The adsorption and photoinitiated dissociation of molecular oxygen on reduced rutile TiO2 nanocluster have been studied using a hybrid density functional theory (DFT)/time-dependent DFT approach and a time-dependent wavepacket dynamics method. Results show that the most favorable state for O2 at the bridging row O-vacancy site of TiO2 is O2(2-) with an orientation parallel to the surface. We find that its dissociation in the electronic ground state involves a spin forbidden intersystem crossing, and therefore has a large barrier along the reaction pathway. However, time-dependent wavepacket calculations reveal that the photoinitiated O2 dissociation on TiO2 is very fast via a direct mechanism on the excited states. The lifetime of excited O2 molecules is predicted to be about 266 fs. Non-adiabatic effects among the singlet electronic states are found to play an important role in the O2 dissociation whereas the spin-orbit effect is negligible. In addition, adsorption of two O2 molecules at an O-vacancy site shows that the second O2 molecule can stabilize the system by about 0.22 eV.