Structure and vibrations of AlnNn (n = 3-9) clusters

The structure and harmonic vibrations of Al(n)N(n) (n = 3-9) clusters have been investigated using the B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional theory. All structures are found to be cumulenic D(nh) rings (equal bonds, alternating angles), with one intense out-of-plane mode and three infrared-active degenerate modes, of which the highest one is extremely intense and asymptotically increases to 1217 cm(-1) for n = 9. Comparisons with C2n clusters and B(n)N(n) clusters, the structure and bonding type for the Al(n)N(n) clusters are consistent with those of the C2n (n = 3, 5, 7, ...) clusters and the B(n)N(n) clusters.