AVS 62nd International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS+AS+EN-TuM

Paper SS+AS+EN-TuM3
Dissociation Dynamics of Energetic Water Molecules on TiO2(110): Combined Molecular Beam Scattering and Scanning Tunneling Microscopy Study

Tuesday, October 20, 2015, 8:40 am, Room 113

Session: Mechanistic Insight of Surface Reactions: Catalysis, ALD, etc. - I
Presenter: Zdenek Dohnalek, Pacific Northwest National Laboratory
Authors: Z.-T. Wang, Pacific Northwest National Laboratory
Y.-G. Wang, Pacific Northwest National Laboratory
R.T. Mu, Pacific Northwest National Laboratory
Y. Yoon, Pacific Northwest National Laboratory
G.A. Schenter, Pacific Northwest National Laboratory
R. Rousseau, Pacific Northwest National Laboratory
I. Lyubinetsky, Pacific Northwest National Laboratory
Z. Dohnalek, Pacific Northwest National Laboratory
Correspondent: Click to Email
Molecular beam scattering techniques have proven extremely useful in determining the dynamics of energy flow in the course of chemical reactions. We have successfully designed and constructed a unique, state of the art instrument combining a molecular beam scattering source coupled with a low temperature scanning tunneling microscope (STM). The combination of these techniques allows us to follow the same area during adsorption and image surface species as a function of incident energy of reacting molecules. Our first study focuses on reversible water dissociation on Ti rows of TiO2(110), which leads to the formation of pairs of terminal and bridging hydroxyl species, H2O ↔ HOt + HOb. The results of our measurements show the onset of H2O dissociation at 0.2-0.3 eV of incident energy, independent of whether the molecules impinge along or across the Ti rows at an incident angle of 60° relative to surface normal. Following the onset, the dissociation probability increases linearly with increasing incident energy. Ensembles of ab initio molecular dynamics (AIMD) simulations at several incident energies reproduce the product distribution seen in the STM. Additionally, these studies show that the dissociation occurs only for the impacts in the vicinity of surface Ti ions with an activation energy of 0.3 eV and that the O-H bond cleavage is accomplished within the time of a single vibration. The AIMD simulations were further used to construct a classical potential energy surface for water/TiO2(110) interactions and execute non-equilibrium classical MD simulations that closely reproduce the onset and linear energy dependence of the dissociation probabilities.