Ab initio correlated calculations of six nitrogen (N6) isomers

Abstract

MP2/6-31G*//MP2/6-31G* structures, energies, and vibrational frequencies have been calculated for six N[sub 6]/isomers. These isomers are the nitrogen analogues of the following carbon structures: benzene, Dewar benzene, benzvalene, triprismane, bicyclopropenyl, and a diazide. They are of interest because there are experimentally known metastable known metastable isoelectronic CH structures in some cases and because of the predicted extremely high-energy content of the nitrogen forms relative to three N[sub 2] molecules. These characteristics make some of the N[sub 6] structures prime candidates as energetic materials. The nitrogen structures are also of interest from the standpoint of quantum-chemical theory because the character (i.e., the number of imaginary vibrational frequencies) of their energy hypersurface stationary points is a strong function of the theoretical model used, e.g., of basis swet quality and/or of whether electron correlation is included in the model. Comparisons are made with a variety of ab-initio models to illustrate this point. 15 refs., 2 figs., 4 tabs.