Identification of Conical Structures in Small Aluminum Oxide Clusters: Infrared Spectroscopy of (Al2O3)1−4(AlO)

• Published in: Journal of the American Chemical Society 2008-11, Vol.130 (45), p.15143-15149
• Main Authors: Santambrogio, Gabriele, Janssens, Ewald, Li, Shaohui, Siebert, Torsten, Meijer, Gerard, Asmis, Knut R, Döbler, Jens, Sierka, Marek, Sauer, Joachim
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja805216e

The vibrational spectroscopy of the electronically closed-shell (Al2O3) n (AlO)+ cations with n = 1−4 is studied in the 530−1200 cm−1 range by infrared predissociation spectroscopy of the corresponding ion−He atom complexes in combination with quantum chemical calculations. In all cases we find, assisted by a genetic algorithm, global minimum structures that differ considerably from those derived from known modifications of bulk alumina. The n = 1 and n = 4 clusters exhibit an exceptionally stable conical structure of C 3 v symmetry, whereas for n = 2 and n = 3, multiple isomers of lower symmetry and similar energy may contribute to the recorded spectra. A blue shift of the highest energy absorption band is observed with increasing cluster size and attributed to a shortening of Al−O bonds in the larger clusters. This intense band is assigned to vibrational modes localized on the rim of the conical structures for n = 1 and n = 4 and may aid in identifying similar, highly symmetric structures in larger ions.