Aiming at a better understanding of the interaction of ionic liquid (IL) thin films with oxide supports, we have performed a model study under ultrahigh vacuum (UHV) conditions. We apply infrared reflection absorption spectroscopy (IRAS) in combination with density functional theory (DFT). Thin films of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf(2)N] are grown on an atomically flat, well-ordered alumina film on NiAl(110) using a novel UHV-compatible evaporator. Time-resolved IRAS measured during the growth and subsequent thermal desorption points toward reversible molecular adsorption and desorption. There was no indication of decomposition. The vibrational bands are assigned with the help of DFT calculations. Strong relative intensity changes in individual [Tf(2)N](-) bands are observed in the monolayer region. This indicates pronounced orientation effects for the anion. The adsorption geometry of [Tf(2)N](-) is determined on the basis of a detailed comparison with DFT. The results suggest that [Tf(2)N](-) anions adopt a cis conformation in the submonolayer region. They adsorb in a slightly tilted orientation with respect to the surface, mainly interacting with the support via the sulfonyl groups.

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We have studied the interaction of water with stoichiometric CeO 2 (111)/Cu(111), partially reduced CeO 2−x /Cu(111), and Pt/CeO 2 / Cu(111) model catalysts by means of synchrotron−radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES) at the Ce 4d edge, infrared reflection absorption spectroscopy (IRAS), and density functional (DF) calculations. The principal species formed during adsorption of water at 160 K on CeO 2 (111) films is chemisorbed molecular water. On the surface of CeO 2−x water partially dissociates yielding hydroxyl groups. By use of core-level PES, differentiation between chemisorbed water and hydroxyl groups is complicated by the overlap of the corresponding spectral features. Nevertheless, we determined three characteristic indicators for OH groups on ceria: (i) the presence of 1π and 3σ states in valence band (VB) PES; (ii) an increase of the binding energy (BE) separation between the O 1s spectral components of lattice oxygen and OH/H 2 O; (iii) an increase of the amplitude of the Ce 3+ resonance in RPES. Chemisorbed water desorbs below 400 K and hydroxyl groups vanish at 500 K. The most favorable configurations of chemisorbed water and hydroxyl groups have been investigated by DF calculations. Both CeO 2 (111) and CeO 2−x involve strongly tilted H 2 O and OH species which complicate their detection by IRAS. On Pt/CeO 2 , water adsorbs molecularly at 160 K but undergoes partial dissociation during annealing. The dissociation of water is accompanied by spillover of hydrogen to ceria and formation of hydroxyl groups between 180 and 250 K. Above 250 K, decomposition of hydroxyl groups and reverse spillover of hydrogen from ceria to Pt occurs, followed by desorption of molecular water.

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We have studied the reaction of NO2 with BaO nanoparticles supported on an ordered Al2O3 thin film on NiAl(110). Combining chemical analysis by X-ray photoelectron spectroscopy (XPS) and vibrational spectroscopy by infrared reflection absorption spectroscopy (IRAS), performed in combination with molecular beam (MB) techniques, the sequence of appearance of various nitrogen−oxo surface intermediates and their spectral properties are identified. The initial intermediates at 300 K are surface nitrites (NO2 -), which are preferentially oriented parallel to the surface. Whereas formation of nitrites is rapid even at 300 K, conversion of nitrites into surface nitrates (NO3 -) occurs at a very low rate. After surface nitrate formation, no further reaction is observed. At higher temperature (500 K), conversion into surface nitrates is more facile and is followed by formation of ionic nitrates. All three nitrogen−oxo species can be clearly identified via their characteristic vibrational spectra. No spectroscopic evidence for the formation of other NO x -derived surface species is found under the reaction conditions applied in this study. The results suggest that (i) conversion of the surface nitrite into the surface nitrate and (ii) formation of the ionic nitrate are the rate-controlling steps in the storage process.