Maria Buchholz

Probing electrons in TiO2 polaronic trap states by IR-absorption: Evidence for the existence of hydrogenic states

An important step in oxide photochemistry, the loading of electrons into shallow trap states, was studied using infrared (IR) spectroscopy on both, rutile TiO2 powders and single-crystal, r-TiO2(110) oriented samples. After UV-irradiation or n-doping by exposure to H-atoms broad IR absorption lines are observed for the powders at around 940 cm−1. For the single crystal substrates, the IR absorption bands arising from an excitation of the trapped electrons into higher-lying final states show additional features not observed in previous work. On the basis of our new, high-resolution data and theoretical studies on the polaron binding energy in rutile we propose that the trap states correspond to polarons and are thus intrinsic in nature. We assign the final states probed by the IR-experiments to hydrogenic states within the polaron potential. Implications of these observations for photochemistry on oxides will be briefly discussed.

The Interaction of Formic Acid with Zinc Oxide: A Combined Experimental and Theoretical Study on Single Crystal and Powder Samples

We present azimuth- and polarization-dependent infrared spectroscopy results obtained under ultra-high vacuum conditions on surface species formed by the interaction of formic acid with the mixed-terminated ZnO(10

Adsorbate-induced lifting of substrate relaxation is a general mechanism governing titania surface chemistry

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Carbon dioxide adsorption on a ZnO(101[combining macron]0) substrate studied by infrared reflection absorption spectroscopy.

1¯0) surface. Since there are no previous IRRAS data for formic-acid derived species on any ZnO single crystal surfaces, we have carried out calculations using density function theory to aid the interpretation of the results. From our combined experimental and theoretical data we conclude that two different formate species are formed. The more strongly bound species is a bidentate with the formate molecular plane oriented along the [1

Carbon dioxide adsorption on a ZnO(100) substrate studied by infrared reflection absorption spectroscopy

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Chemical activity of oxygen vacancies on ceria: a combined experimental and theoretical study on CeO2(111).

2¯10] direction. The less strongly bound species is a quasi-bidentate with its molecular plane oriented along the [0001] direction. This second species is characterized by a strong hydrogen bond between a surface OH species and the formate. In addition, IR data were recorded for the same molecule adsorbed on commercial ZnO nanoparticles. The different bands of the powder IR-data are assigned on the basis of the experimental and theoretical results obtained for the single crystal surface. This study demonstrates the importance of the Surface Science approach to heterogeneous catalysis also for ZnO, an important catalyst for the conversion of syngas to methanol.