An ab initio study of potential energy surfaces for N-8 isomers

The potential energy surfaces and the nature of transition structures for t he decomposition of three Ns isomers (octaazapentalene, azidopentazole, and diazidodiimide) into 4 N-2 are investigated using ab initio methods. These isomers are all high-energy species, relative to molecular nitrogen, but a re much lower in energy than the previously studied cubic structure. Second -order perturbation theory (MP2) predicts that the dissociation of octaazap entalene proceeds via isomerization to a linear molecule. The dissociation reaction of azidopentazole prefers ring breaking, at a cost of less than 20 kcal/mol, to breaking a bond in the side chain. The cis isomer of diazidod iimide is found to be slightly more stable than that of the trans isomer at the highest levels of theory used here. The coupled cluster (CCSD(T)) diaz idodiimide dissociation barrier is computed to be about 20 kcal/mol. This b arrier is only marginally sufficient to make this high energy density molec ule metastable.