Gas-Phase Vibrational Spectroscopy of the Aluminum Oxide Anions (Al₂O₃)_1-6AlO₂^-

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 C3v ground state structure. Locating the global minima of the larger systems proves challenging