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 alumina manifests 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. Alumina goes amorphous: The structures of aluminum oxide anions in the gas phase are studied using cryogenic ion‐trap vibrational spectroscopy in combination with density functional theory. The average coordination numbers for the series (Al2O3)1–6AlO2− increase with cluster size and approach those reported for amorphous alumina already for clusters containing a few tens of atoms.