On the structure and stability of geometrical isomers of N3F

Abstract

The potential energy surfaces for the N3F molecule have been studied using multiconfigurational wave functions. Two new isomers were found, one on the singlet (1A′) and one on the triplet (3A″) surface. Both isomers have a three-membered cyclic structure and Cs symmetry. The singlet cyclic isomer is endoergic relative to the open fluorine azide by 15–17 kcal/mol. Its kinetic stability is close to the stability of the open isomer: the barrier separating the cyclic isomer from the dissociation products N2(X 1Σ+g)+NF(a 1Δ) is about 13–17 kcal/mol and is lower than the barrier to isomerization. The triplet cyclic isomer is much higher in energy (about 70 kcal/mol), with a barrier to dissociation to N2(X 1Σ+g)+NF(X 3Σ−) on the order of 15 kcal/mol. Crossings of the 1A′ and the 3A″ surfaces may allow the cyclic singlet isomer to predissociate to the ground state products, N2(X 1Σ+g)+NF(X 3Σ−). It is shown, however, that the singlet–triplet surface of intersection lies ‘behind’ the barrier to singlet decomposition, so that spin-forbidden predissociation will not preclude detection of cyclic N3F.