Electronic States of Aminonitrene (1, 1-Diazine). A Study of the Endwise Bonding of Dinitrogen

The ground and excited states of aminonitrene (1, 1-diazine), H₂NN, were studied using generalized valence bond (GVB) and configuration interaction (GVB-CI) wave functions. We find that the ground state is a singlet state (¹A_O with the triplet (³A₂) lying 15 kcal/mol higher. (In the Hartree-Fock description, the triplet state is 5 kcal below the singlet, indicating the necessity of including electron-correlation effects.) The stabilization of the singlet state is due to a large amount of double bond character in the NN bond (H₂N+⩵N:-) as reflected in the short bond length (Re=1.25 Å) and the large dipole moment (μ=4.036 D). In contrast, the 3A2 state has Re=1.37 A and μ=2.35 D. With extensive CI we find an NN bond energy of D0(H₂NN)=69 kcal/mol, leading to a heat formation of ΔH_f298K(H₂NN)=90 kcal/mol. The character of higher excited states and ions is also discussed. Some predictions of the thermochemistry of 1, 1-diazines are provided.