Contributions to the vibrational energy demonstrated in Fig. indicate, that at the initial RS state, most of the energy change is localized in the NH2 group, and it is distributed in nearly equal parts between N1-H4 and H5-N1 bonds, with a small admixture from N1-C2 bond (Fig. ). The situation is only partially reversed in the final PS state: the energy change is localized largely in H4-O3 bond, however, the share of N1-H5 bond is recovered, after falling to zero near TS. The N1-C2 skeleton bond follows this trend, reaching at PS the level considerably higher than it has been at RS (Fig. ), as its formal bond order is increased.