Vibrational Spectroscopy of Aluminum Oxide Cluster

Vibrational Spectroscopy of Aluminum Oxide Cluster Anions: Structure and Reactivity Xiaowei Song,
1,2
Matias R. Fagiani,
1,2
3
1
1
Florian A. Bischoff, Wieland Schöllkopf, Sandy Gewinner, 3
1,2
Joachim Sauer and Knut R. Asmis 1
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany. 2
3
Wilhelm-Ostwald-Institut, Universität Leipzig, Linnéstr. 2, 04103 Leipzig, Germany Institut für Chemie, Humboldt-Universität Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany Aluminum is the most abundant metal element in Earth’s crust and its oxide forms contribute a significant
fraction to various natural environments and play important roles in biogeochemical reactions. They are
also of particular interest in industrial applications, as ceramics, abrasives, absorbents, catalysts and
supports for catalysts. However, a molecular level understanding of their material development from small
clusters containing a few atoms to nanoparticles is still lacking. Spectroscopic studies on size-selected gas
phase clusters [1.2] can aid in gaining insight into the concepts governing these processes. Here, we use
infrared photodissociation (IRPD) in combination with the intense and widely-tunable radiation from the
IR free electron laser FHI-FEL [3] to study the structure and reactivity of aluminum oxide cluster anions
in the gas phase. The nominally electronic closed shell clusters (AlO2)(Al2O3)-x=0-6 as well as the small
mono-, bi- aluminum clusters AlO-x=1-4 and Al2O-x=3-6 are probed. Structures are assigned based on a
comparison of the IRPD spectra of the (H2)D2-tagged cluster anions to simulated IR spectra from
electronic structure calculations. The terminal Al-O stretching modes involving singly-coordinated oxygen
atoms are found in-between 950 and 1200 cm-1. Al-O stretching modes involving doubly- and triplycoordinated O-atoms lie lower in energy (600-950 cm-1) and O-Al-O bending modes are found below 600
cm-1. For some of the open-shell cluster anions reactions with the H2-messenger molecules are observed.
The underlying reaction mechanism will be studied in more detail in our ion trap setup, i.e., rate constants.
In the next step, we will probe the microhydration and/or reaction with water of selected aluminum oxide
clusters, namely (Al3O4)+ and (Al2O3)4-.
References [1] G. Santambrogio, E. Janssens, S. Li, T. Siebert, G. Meijer, K.R. Asmis, Jens Döbler, M. Sierka, J.
Sauer, J. Am. Chem. Soc. 130, 15143-15149 (2008). [2] Sierka, J. Döbler, J. Sauer, G. Santambrogio, M. Brümmer, L. Wöste, E. Jannsens, G. Meijer, K.R.
Asmis, Angew. Chem. Int. Ed. 46, 3372-5 (2007). [3] Schöllkopf, W., Gewinner, S., Erlebach, W., Heyne, G., Junkes, H., Liedke, A., et al. (2013). In
Proceedings of FEL 2013, New York, NY, USA (pp. 657-660).