NEW ISOMERS OF N-8 WITHOUT DOUBLE-BONDS

Quantum mechanical methods have been used to examine isomers of N-8. I n addition to the previously studied octaazacubane structure (O-h symm etry, 1), we have investigated two new structures, of D-2h (2) and C-2 v (3) symmetry, without N=N double bonds. The C-2v structure may be de signated octaazacuneane. The following basis sets and methods have bee n employed to optimize geometries: (1) (SCF, CISD, CCSD)/DZP; (2) (SCF , MP2, B3LYP, B3P86, BHLYP)/6-31G; (3) B3LYP/6-311+G*. The single-poi nt energies have also been estimated at the CISD+Q/DZP level of theory with CISD/DZP geometries and at the CCSD(T)/DZP level with CCSD/DZP g eometries. The harmonic vibrational frequencies and their infrared int ensities have also been predicted with the SCF, MP2, and DFT methods. The results show that the two new isomers are both minima on the Ng po tential energy hypersurface and of higher energy than isomers containi ng N=N double bonds. Among the three isomers with only single bonds, t he ones with the higher symmetry have higher energies.