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 Dnh rings (equal bonds, alternating angles), with one intense out-of-plane mode and three infrared-active degenerate modes, of which the top one is extremely intense and asymptotically goes to about 2040 cm− for high n. SCF calculations perform relatively well (especially for n odd), contrary to the isoelectronic C2n clusters. As n increases, the NBN angle approaches 180°. The isoelectronic principle is seen to be followed only partially (odd n) for the similarity between BnNn and C2n clusters.