Potential energy surface of the photolysis of isocyanic acid HNCO

The dissociation curves of the photolysis of the isocyanic acid corresponding to the ground state (S₀) the first triplet excited state (T₁) and the first singlet excited state (S₁) have been studied respectively at the UHF/6-311G^** and CIS/6-311G^** levels usingab initio method. The energy surface crossing points, S₁/T₁, T₁/S₀ and S₁/S₀, have been found and the characteristics of the energy minimum crossing point were given, based on which, the changes of the crossing points’ geometries along the lower electronic energy surface and its end-result have been located according to the steepest descent principle. The computational result indicates that the photolysis of the isocyanic acid has three competitive reaction channels ((A)—(C)), and from the kinetic piont of view, channel (A) is the most advantageous.