A THEORETICAL DETERMINATION OF THE DISSOCIATION-ENERGY OF THE NITRIC-OXIDE DIMER

Multi-reference CI methods have been applied to determine the dissociation energy and structure of the cis-N2O2 molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional (ACPF) approach. The optimal geometry computed at this level was found to be: r(NN)=2.284 angstrom, r(NO) = 1.149 angstrom, and <NNO=96.1-degrees. Employing the [6s5p3d2f] basis set, the BSSE was found to be almost-equal-to 2 kJ/mol.