Photodesorption of water from rutile(110): ab initio calculation of five-dimensional potential energy surfaces of ground and excited electronic states and wave packet studies

Abstract

In this paper, we report on our results concerning the interaction of water with titanium dioxide in its rutile modification. The (110) surface is modelled by an embedded Ti9O18Mg7(14+) cluster. We present up to five-dimensional potential energy surfaces for the water molecule on this surface and include the dissociation of one hydrogen atom. The electronic ground state as well as one electronically excited state is included. To deal with the multi-configurational character of the wave function, we use the complete active space self-consistent field (CASSCF) approach. The resulting potential energy surfaces are fitted by means of an artificial neural network. As a first example of quantum dynamical studies based on our potential surfaces, we present results on the photodesorption of water from rutile(110).

Photodesorption of H2O from Anatase-TiO2(101): A Combined Quantum Chemical and Quantum Dynamical Study

“…For long resonance lifetimes of the CT state of about 240 fs, this rate converged to a value of 85%, irrespective of the vibronical excitation. In comparison with previous simulations on the H 2 O/r-TiO 2 (110) system, which exhibit converged photodesorption probabilities of 82%, 41 both modifications presumably exhibit similar properties with regard to this prototype of a photoreaction. However, for r-TiO 2 (110), the velocity distribution of the desorbed molecules revealed a sharp peak at 4600 m s −1 , whereas in our study, a-TiO 2 (101) features a bimodal distribution with much smaller velocities of 1650 and 2000 m s −1 .…”

“…In addition, vibronically excited wavepackets do not significantly alter this finding and only show a small decrease in this probability of 81%. In comparison to previous work on the photodesorption of H 2 O from r-TiO 2 (110) by Mitschker et al, which found a converged desorption probability of 82% for large resonance lifetimes, both materials presumably exhibit similar properties regarding the photodesorption dependence on the lifetime of the CT state.…”

“…Since the energetics of this electron transfer are experimentally not accessible, we first compare our active space setup to the more readily available HOMO–LUMO transition of the water molecule in the gas phase. A broad spectrum of active spaces for the water molecule were already studied for the H 2 O/r-TiO 2 (110) system . For the water molecule on its own, it could be shown that the active space sizes of CAS­(6,5) and CAS­(8,6) perform best compared to those of experiment.…”

“…A broad spectrum of active spaces for the water molecule were already studied for the H 2 O/r-TiO 2 (110) system. 41 For the water molecule on its own, it could be shown that the active space sizes of CAS (6,5) and CAS (8,6) perform best compared to those of experiment. These results were tested against our H 2 O/a-TiO 2 (101) system with the water molecule at a far noninteracting distance using CASSCF/N-electron valence secondorder perturbation theory (NEVPT2) (see Table 1).…”

Adsorption and Photodesorption of CO from Charged Point Defects on TiO2(110)

“…To verify this, we used cutoff optical filters with the UV source and did not observe any CO photodesorption for photon energies below the TiO 2 band gap (∼3.1 eV), the threshold for the electron–hole generation. Direct photoexcitation and desorption of the adsorbed CO molecule requires more than a 6 eV photon energy, − which cannot be achieved in our experiments with a mercury lamp source.…”