Semiempirical VB Calculation of the (H2I2) Interaction Potential

A simple, nonionic valence‐bond formalism is employed to obtain the interaction potential energy for the (H₂I₂) system. The system is treated as one consisting of four electrons moving in the potential of two nonpolarizable I⁺ cores and two protons. All three‐ and four‐center integrals are omitted to obtain the London expression for the system potential. All remaining Coulomb and exchange integrals are evaluated semiempirically in terms of ground state ${}^1\Sigma$ and lowest triplet ${}^3\Sigma$ state potentials by utilizing the Heitler–London expression for the energy of the diatomic systems. The result is a closed‐form analytical expression for the system potential energy as a function of the six interparticle distances. Potential‐energy contour maps are presented for the $C_{\text{2υ}}$ and distorted planar trapezoidal conformations, symmetric and nonsymmetric linear arrangements, and a planar “staggered” conformation. The three‐body (H₂I) potential‐energy surface is also investigated and contour maps for the 90° and linear surfaces are given.