The electronic structure of N2O4. I. σ-Electron delocalization study

A detailed molecular orbital study of the σ- and π-electrons of N2O4 is described. Special consideration is given to possible types of oxygen σ-electron delocalization into antibonding NK and KO orbitals which are vacant in the classical structure. Of these, only depopulation of oxygen 2pπ-orbitals into the antibonding NN σ-orbital seems to be of overall importance for interpreting the NN and NO bond properties. The other oxygen a-electron delocalizations are small, and their contributions to the NO bond orders (although sometimes significant), appear largely to cancel. The possibility that our VESCF procedure may yield an overestimate in the magnitude of the calculated NN σ-bond-order is discussed. A distinction is made between the nature of molecular orbitals arising from combination of π-orbitals on oxygen with the antibonding NN and the antibonding NO orbitals respectively.