B3LYP calculations of the potential energy surfaces of the thermal dissociations and the triplet ground state of pyrolysis products XN(x̃ 3Σ−) for halogen azides XN3 (X: F, Cl, Br, I)

Mechanisms of XN3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN3(x̃ 1A′) and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN3(x̃ 1A′)→XN(a 1Δ)+N2(x̃ 1Σg+). The ISC point, therefore, is considered as a ‘transition state’ of the spin-forbidden reactions, XN3(x̃ 1A′)→XN(x̃ 3Σ−)+N2(x̃ 1Σg+). The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied.