AN AB-INITIO STUDY OF THE STRUCTURES OF CYCLIC N4O2

The structures of the cyclic N4O2 molecule are investigated using thre e levels of nb initio electronic structure methods. Hartree-Fock self- consistent-field (SCF), second-order Moller-Plesset perturbation theor y (MP2), and quadratic configuration interaction including single and double substitutions (QCISD) calculations are performed employing two basis sets of double-zeta plus polarization (DZP) and a triple(plus)-z eta double polarization (TZ-2P) quality. Two structures are located. A boat conformation (C-2v structure) is determined to be a minimum equi librium structure with exothermicity of similar to 80, 140, and 100 kc al/mol relative to dissociation to 2N(2)O, 2N(2) + O-2, and 2NO + N-2, respectively. A planar (D-2h, structure) previously reported to be a minimum [Jones, W. H. J. Phys. Chem. 1992, 96, 5184] is confirmed in t his study to be a transition state (saddle point) lying similar to 7-1 0 kcal/mol above the boat minimum as calculated at all levels of theor y. A search for a chair and a twisted conformation has proven unsucces sful. Harmonic vibrational frequencies and infrared intensities are re ported for both optimized boat and planar structures at all levels of theory. The consideration of the stable form of this molecule as a hig h energy density-material is discussed.