STRUCTURE AND VIBRATIONS OF BNNN (N=3-10)

The structure and harmonic vibrations of BnNn clusters (n = 3-10) have been investigated using density functional theory with exact-exchange contributions. All structures are found to be cumulenic D-nh rings (e qual bonds, alternating angles), with one intense out-of-plane mode an d three infrared-active degenerate modes, of which the top one is extr emely intense and asymptotically goes to about 2040 cm(-1) for high n. SCF calculations perform relatively well (especially for n odd), cont rary to the isoelectronic C-2n clusters. As n increases, the NBN angle approaches 180 degrees. The isoelectronic principle is seen to be fol lowed only partially (odd n) for the similarity between BnNn and C-2n clusters.