VALENCE-BOND STUDIES OF THE D-2H ISOMER OF O-4 - AN INTERIM-REPORT

Single-zeta and pi-electron double-zeta basis sets are used to examine some theories of the origin of the stability of the D-2h isomer of O- 4, using ab initio valence-bond procedures. With these basis sets, res onance between covalent-type (i.e., O-2 .. O-2) valence-bond structure s does not lead to a stabilization of the dimer relative to the separa ted monomers. When basis sets of the same size are used to construct w ave functions for covalent and ionic structures, covalent-ionic resona nce (i.e., O-2 ... O-2 <-> O-2(+) .. O-2(-) <-> O-2(-).. O-2(+)) is al so unable to stabilize the dimer. Without consideration of the basis-s et superposition error, stability is obtained when the size of the AO basis is increased for the dimer relative to the monomer, either via t he basis for the ionic structures or by the inclusion of midbond funct ions. Brief consideration is given to an increased-valence structure f or the dimer. (C) 1997 John Wiley & Sons, Inc.