Structural Investigations of Aluminum Cluster Ions, Al_n^-(n = 3–50)

Laser ablation of a flat aluminum metal target (without using the bath gas/supersonic expansion technique) was used to generate aluminum cluster anions containing from 3 to 50 atoms. The structures and reactivities of Al_n^-for n = 3–23 were then probed with the use of Fourier transform mass spectrometry. Charge exchange reactions were used to bracket the electron affinities of these clusters, which were in good agreement with other theoretical and experimental values. Collisional dissociation of Al_n^-for n = 3–13 indicated elimination of neutral aluminum atoms for all cluster ions, except Al₇^-, Al₆^-, and Al₃^-, which fragmented primarily by electron detachment. Aluminum cluster ions are unreactive with CH₄ and N₂0, but the small cluster ions will react with O₂ to generate AlO₂^-and AlO^-. For clusters containing more than eight aluminum atoms, the even-numbered clusters react much more rapidly than the odd-numbered clusters with oxygen to form AlO₂^-and AlO^-.