Gas-Phase Vibrational Spectroscopy of the Aluminum Oxide Anions (Al O ) AlO.

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 (Al O ) AlO with n=1-6. The infrared photodissociation spectra of the D -tagged complexes, measured in the fingerprint spectral range (400-1200 cm ), 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 ground-state structure. Locating the global minima of the larger systems proves challenging.