A theoretical investigation of the structure and bonding of diazomethane, CH2N2

We have investigated the electronic ground-state structure and binding mode of CH2N2 by ab initio multireference perturbation calculations CASPT2 and CASPT3, using correlation consistent cc-pVTZ basis sets. Our calculations suggest that the CH2-N-2 binding between the CH2 ((a) over tilde(1)A(1)) and N-2 (X(1)Sigma(g)(+)) moieties consists of a "harpooning" sigma, bond from Nt to CH2 and a pi-like bond due to the back-transfer of electrons from CH2 to N-2. Despite the popular dipolar resonance structures employed to represent the CH2N2 binding no charge transfer between the in situ CH2 and N-2 is observed. Our CH2-N-2 dissociation energy is D-e = 38.2 kcal/mol with respect to the CH2 ((a) over tilde(1)A(1)) + N-2 (X(1)Sigma g(+)) adiabatic products or D-e = 27.2 kcal/mol with respect to the ground (X) over tilde(3)B(1) state of CH2. Taking into account zero point energy corrections, this value is reduced to D-o = 21.6 kcal/mol.