Theory of the Relation between Bond Length and Bond Order by an Extended INDO Method

Abstract

We consider a system consisted of even valence-shell electrons according to the LCAO-ASMO-SCF theory, and we first point out that the extended INDO method proposed by Sugimoto et al. Can systematically be formulated by taking account of the zeroth- and first-order effects in respect to overlap integral S_μ(A)ν(B) between atomic orbitals (μ, ν) on bonded atoms (A, B) . On this basis, the approximate expression of ground-state configuration energy E_g is divided into several parts using π - and σ -type bond orders, and a general relation between bond length and bond order is derived by approximating S_μ(A)ν(B) and two-center Coulomb integral γ_s(A)s(B) (s denoting 1s- or 2s-orbital) as quadratic functions of bond length R_{[AB]} . Finally, the reasonability and usefulness of this relation are discussed in §5.