N4 Singlet Potential Energy Surface

Another possible reaction channel for the decomposition of 1 involves the isomerization into N4(X 2/,) (3). In the Dj symmetry group the electronic configurations of 1 and 3 differ in the occupation of the 5a and 4b2 orbitals [(5a)2(4b2)° in 1 and (5a)°(4b2)2 in 3]. In a recent study, we located the minimum crossing point (4TS) for these two configuration to be 70 kcal/mol above 1 at the CAS(8,8)/cc-pVTZ level [19], Unfortunately, we were not able to locate a true transition state for the process. Korkin et al. also located the minimum crossing in D2 symmetry, and computed the barrier to 70 kcal/mol at the MP2/6-31+G level [24]. Thus, we can safely conclude that the 

We recently investigated the potential energy surface for dissociation of 3 at the CAS(12,12) level [19]. The dissociation process was found to proceed via a transition state of C2V symmetry (5TS). Earlier studies had proposed a D2h transition state [24, 29], however, it was shown that the D2h structure is a second order saddle point rather than a transition state. Single point calculations at 

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Fig. 1. Optimized geometries of stationary points on the N4 singlet potential energy surface.

Fig. 2. Relative energies in kcal/mol at 0 K for stationary points on the N4 singlet potential energy surface. The energies are best estimates based on CCSD(T), MR-CI and CAS-SCF calculations reported in Ref [17, 19, 26, 27]. Note that the spin-forbidden dissociation pathway that passes via the minimum crossing point 7S-T is included. This pathway is discussed in the section (2.2) on the N4 triplet potential energy surface.. ...

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