An ab initio study on the equilibrium structure and torsional potential energy function of dinitrogen tetroxide

The molecular parameters of dinitrogen tetroxide, N2O4, have been determined in large-scale ab initio calculations using the multiconfigurational second-order perturbation method, CASSCF/CASPT2, and basis sets of double- to quadruple-zeta quality. With the largest basis set employed, cc-pVQZ for nitrogen and cc-pVTZ for oxygen, the structural equilibrium parameters are determined to be r(NN) = 1.7940 Å, r(NO) = 1.1906 Å and ∠(NNO) = 112.55°. The potential energy barrier at the staggered conformation of the molecule is found to be 2313 cm−1, and the binding energy of the NN bond is calculated to be 4616 cm−1 (13.2 kcal/mol).