A theoretical study of the azide (N3) doublet states. A new route to tetraazatetrahedrane (N4): N+N3→N4

Abstract

The potential energy surfaces for the low-lying doublet states of the azide radical (N3) have been computed at the complete active space self-consistent field (CASSCF) level with the CAS(15,12) active space. The cc-pVTZ and aug-cc-pVTZ basis sets have been employed throughout the present work. Energies, geometries and harmonic frequencies were determined for the N3 linear ground electronic state (2Πg), a stable C2v ring structure (2B1), and a Cs transition state (2A″) connecting the ring and linear structures. Other N3 (C2v) stationary points (2A2, B12, and A12) have been characterized, as well. The vertical excitation energies for the doublet excited states of the N3 linear (2Πg) and stable ring (2B1) isomers were calculated using CASSCF and multireference configuration interaction [MRCI-SD(Q)] methods. A new route to tetraazatetrahedrane [N4(Td)] has been proposed on the N4 singlet potential energy surface within Cs symmetry. MRCI-SD(Q) calculations predict that N4 (Td) can be formed from atomic nitrogen in the D2 state and N3 (C2v, B12) in a barrierless exothermic reaction. The energy difference (D0) is 135.4 kcal/mol at the MRCI-SD(Q) level.