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

Multi-reference CI methods have been applied to determine the dissocia tion 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 wav e function. The best calculated value, 13.8 kJ/mol, is in agreement wi th the experimental value, 12.2 kJ/mol. It has been obtained with an e xtended ANO-type basis set [6s5p3d2f], including the effect of the bas is set superposition error (BSSE) in the geometry optimization, and ad ditional effects, such as the electron correlation of core electrons a nd relativistic corrections, using the average coupled pair functional (ACPF) approach. The optimal geometry computed at this level was foun d to be: r(NN)=2.284 angstrom, r(NO) = 1.149 angstrom, and <NNO=96.1-d egrees. Employing the [6s5p3d2f] basis set, the BSSE was found to be a lmost-equal-to 2 kJ/mol.