Stuttgart 2012 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 46: Cluster

A 46.2: Vortrag

Freitag, 16. März 2012, 10:45–11:00, V38.02

Structural Variability in Transition Metal Oxide Clusters: Gas Phase Vibrational Spectroscopy of V₃O₆₋₈⁺ — •Claudia Brieger¹, Torsten Wende¹, Jens Döbler², Andrzej Niedziela², Joachim Sauer², Gerard Meijer¹, and Knut R. Asmis¹ — ¹Fritz-Haber Institut der MPG, Berlin — ²Humboldt Universität Berlin

Vanadium oxides exhibit a high structural variability and redox activity which comes to play into heterogeneous catalysis. Interestingly, the structure of the active sites in vanadium oxide catalysts is often not well known. Infrared photodissociation (IRPD) spectroscopy can be used to obtain structural information on isolated clusters in the gas phase. Here, we study the structures of tri-nuclear vanadium oxide cations. IRPD spectra of V₃O₆⁺He₁₋₄, V₃O₇⁺Ar₀₋₁, and V₃O₈⁺Ar₀₋₂ from 350 to 1200 cm⁻¹ are presented. V₃O₇⁺ and V₃O₈⁺ have a cage-like structure whereas a chain isomer is found to be most stable for V₃O₆⁺. The binding of the rare gas atoms to V₃O₆₋₈⁺ clusters is found to be strong, up to 58 kJ/mol for Ar, and markedly isomer-dependent, resulting in two interesting effects. First, for V₃O₇⁺Ar₁ and V₃O₈⁺Ar₁ an energetic reordering of the isomers compared to the bare ion is observed, making the ring-motif the most stable one. Second, different isomers bind different number of rare gas atoms. We demonstrate, how both effects can be exploited to isolate and assign the contributions from multiple isomers to the IR spectrum. The present results exemplify the sensitivity of the structure of vanadium oxide clusters on small perturbations in their environment.