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Abstract

We use cryogenic ion trap vibrational spectroscopy in combination with density functional theory to probe, how the structural variability of aluminas manifest itself in the structures of the gas phase clusters (Al₂O₃)_nAlO₂^- with n = 1-6. The infrared photodissociation spectra of the D₂-tagged complexes, measured in the fingerprint spectral range (400-1200 cm^-1), are rich in spectral features and start approaching the vibrational spectrum of amorphous alumina particles for n > 4. Aided by a genetic algorithm, we find a trend towards the formation of irregular structures for larger n, with the exception of n = 4, which exhibits a C_3v ground state structure. Locating the global minima of the larger systems proves challenging.