Ab initio valence bond calculations for the ground state of ozone

Abstract

The results of ab initio valence-bond calculations, with an STO-6G basis set, are reported for the ground state of ozone. Both Heitler-London and localized molecular-orbital procedures have been used to construct the wavefunctions for the a-bonds. Hybridization of the orbitals on each atom has been determined by energy considerations.In accord with previous results, the primary Lewis structure is calculated to be the spin-paired diradical structure ( 6 ) with two a-bonds, and a long, or formal, .rr-bond associated with the terminal atoms. However, the sum of weights for four Lewis structures (11)-( 14), which arise from polarization of either a-bond in (6), is calculated to exceed the weight for (6).Particular attention is given to the calculation of energies for 'increasedvalence' structures (1) and (2), which are constructed by spin-pairing the two unpaired electrons of ground-state O2 with those of a ground-state oxygen atom. If a two-centre molecular orbital is used to accommodate the two electrons of the 0-0 a-bond in each of these structures, then resonance between these structures is equivalent to resonance between numerous Lewis structures including (6) + (11)-( 14), when Heitler-London procedures are used to formulate the wavefunctions for all electron-pair bonds in the Lewis structures. The results of calculations which utilize this approach indicate that resonance between increased-valence structures provides the primary valence bond representation for the O3 ground state. Such structures are stabilized slightly by interaction with the Lewis structures that involve excited states for the 0 atom and the O2 molecule. The resulting energy for resonance between these four valence-bond structures lies at least 0.134 au below the STO-6G RHF-MO energy of -224.091 au.

On the Singlet Diradical Character of S2N2

“…Each of the calculations of (f)−(h) involves six singly occupied π-electron orbitals, as there are in ref . The appropriate S = 0 spin wave function for the resulting six-orbital (φ 1 , φ 2 )(φ 3 , φ 4 )(φ 5 , φ 6 ) configuration may be developed from (φ i , φ j ) and corresponds to that which is presented in ref , for example. Results of all calculations, with variationally determined values for the polarity parameter k for the S−N σ bonds, are reported in Table .…”

The 1 : 1 Adduct of 1,3-Diisopropyl-4,5-dimethyl-2,3-dihydroimidazol-2- ylidene and Nitrous Oxide

“…The increased-valence structure 1d [6] with one electron π x (NO) and π y (NO) bonds and two fractional π x (NN) π y (NN) bonds has also been suggested to describe the N 2 O geometry and chemical behavior. The qualitative VB treatment indicates electrophilic character at both N atoms (Scheme 1).…”