Partial potential energy diagram for the C₃N₂ system on the triplet surface calculated at the M06-2X/AVTZ level including ZPE. The C₃ + N₂ exit channel in red is spin forbidden if C₃ and N₂ are in their singlet ground state. We cannot find the TS from NC-c.CC=N toward NC-c.C=NC at M06-2X/AVTZ level, both specieshaving very similar structure (two different cyclic isomers with slightly different geometries and energies). NC-c.CC=N is a local minimum but directly connected to NC-c.C=NC without barrier at semi-empirical AM1 level. So, this TS is very likely close in energy to NC-c.CC=N.