Theoretical study of metastable N 2CO isomers. New candidates for high energy materials?

Abstract

The geometries, energies and frequencies of singlet and triplet N 2CO isomers were computed ab initio at the HF/6-31G *, MP2/6-31+G * and at the BECKE3LYP/6-311+G * levels. Single point energies were calculated at the QCISD(T)/6-311+ G *//MP2/6-31+G * level and at the CCSD(T)/6-311+G(2D)//BECKE3LYP/6-311+G * level. The most stable bound N 2CO isomer is the unknown three-membered cyclic C 2v structure (diazirinone); its aromatic stabilization energy is only 7 kcal/mol. Dissociation of diazirinone into N 2 and CO is exothermic by 96–100 kcal/mol, but the 27 kcal/mol barrier is sufficiently high to permit observation. The open-chain NNCO triplet lies 5 kcal/mol above diazirinone and ≈ 35 kcal/mol below the spin-allowed dissocition into X 1Σ + g N 2 and 3Π r CO. While the known nitrosyl cyanide (NCNO) is 11 kcal/mol less stable than diazirinone, the dissociation into CN and NO radicals is endothermic by 47–50 kcal/mol.