Structure and stability of N-6 isomers and their spectroscopic characteristics

Among homonuclear nitrogen molecules, Ng isomers occupy a critical position as a possible diazide or a benzene analogue. However, the character of sta tionary points on the N-6 potential-energy hypersurface is known to be a st rong function of choice of calculation methods and basis set. We present re sults with density functional theory (B3LYP and PW91 functionals) and coupl ed cluster theory (CCSD(T)) to investigate the shape of the potential-energ y surface. The CCSD(T) suggests fewer minima on the potential-energy surfac e compared with the density functional theory. The stability and amount of internally stored energy of Nd isomers as well as their spectroscopic chara cteristics are important. Structure, vibrational frequencies including IR a nd CCSD Raman intensities, heats of formation, vertical ionization potentia ls, electron affinities, and excitation energies are reported.