Geometries of O4+, O4−, and N4+ by an Approximate SCF–MO Theory Which Considers Intermolecular Differential Overlap

Abstract

We have found that the CNDO/2 (semiempirical SCF–MO) theory does not properly account for the long-range repulsive interactions in O2–O2 (S = 2) and O2–O2+ (S = 32). This results in the O2–O2 interaction potential being zero at O–O separations of 2.3–3.5 Å and the O2–O2+ bond energy being much too large. The CNDO/2 method has been modified by considering sp-type integrals to account for charge–quadrupole and charge–atomic polarization interactions. In addition, differential overlap is considered and multicenter integrals are approximated for intermolecular interactions. This is a semiempirical method in which the adjustable constants are fixed by the quadrupole moments of O2 and N2 and the O4+ bond energy. The interaction energies of O4+, O4−, and N4+ are computed for structures of C2 symmetry as a function of θ and R. The equilibrium dissociation energies De (kcal) at Re (Å) and θe are as follows: O4+, 11.66, 2.03, − 67°; O4−, 8.49, 2.08, − 71°; N4+, 34.7, 2.04, O°. The computed O2–O2 interaction potential is in reasonable agreement with the experimental results for the repulsive part of the van der Waals potential.