Characterization of water dissociation on α-Al2O3(11[combining macron]02): theory and experiment.
The interaction of water with α-alumina (i.e. α-Al2O3) surfaces is important in a variety of applications and a useful model for the interaction of water with environmentally abundant aluminosilicate phases. Despite its significance, studies of water interaction with α-Al2O3 surfaces other than the (0001) are extremely limited. Here we characterize the interaction of water (D2O) with a well defined α-Al2O3(11[combining macron]02) surface in UHV both experimentally, using temperature programmed desorption and surface-specific vibrational spectroscopy, and theoretically, using periodic-slab density functional theory calculations. This combined approach makes it possible to demonstrate that water adsorption occurs only at a single well defined surface site (the so-called 1-4 configuration) and that at this site the barrier between the molecularly and dissociatively adsorbed forms is very low: 0.06 eV. A subset of OD stretch vibrations are parallel to this dissociation coordinate, and thus would be expected to be shifted to low frequencies relative to an uncoupled harmonic oscillator. To quantify this effect we solve the vibrational Schrödinger equation along the dissociation coordinate and find fundamental frequencies red-shifted by more than 1500 cm(-1). Within the context of this model, at moderate temperatures, we further find that some fraction of surface deuterons are likely delocalized: dissociatively and molecularly absorbed states are no longer distinguishable.
Institute of Chemistry, University of Potsdam, Karl-Liebknecht Straße 24-25, D-14476 Potsdam, Germany.
Jonas
J
Wirth
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany. campen@fhi-berlin.mpg.de.
Harald
H
Kirsch
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany. campen@fhi-berlin.mpg.de.
Sebastian
S
Wlosczyk
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany. campen@fhi-berlin.mpg.de.
Yujin
Y
Tong
Institute of Chemistry, University of Potsdam, Karl-Liebknecht Straße 24-25, D-14476 Potsdam, Germany.
Peter
P
Saalfrank
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany. campen@fhi-berlin.mpg.de.
R Kramer
RK
Campen