Valence bond study of hyperfine interactions and structure of the noble gas monohalides

Abstract

A semiempirical valence bond (VB) wavefunction that includes correlation between electrons of opposite spin is used to calculate hyperfine structure constants (hfc) of the noble gas monohalide molecules (NX). This wavefunction has the form ψ =N (2Σ)[χ𝒜Φ (N⋅⋅⋅X)+(1−χ2)1/2 𝒜Φ (N+⋅⋅⋅X−)] where N and X denote the noble gas and halogen, respectively, and 𝒜 is the antisymmetrization operator. This antisymmetrization and the effects of interatomic electron correlation on open shell states are the major contributors to the isotropic hfc. These correlation effects are treated by perturbation theory calculations of the van der Waals polarization of X by N in the VB structure Φ (N⋅⋅⋅X) and the Coulomb polarization of N+ by X− in Φ (N+⋅⋅⋅X−). It is also important to consider both valence and inner shell s electrons, and to include intra-atomic electron correlation. The latter is treated by using neutral atom orbitals for N and X in Φ (N⋅⋅⋅X) and cation and anion orbitals for N+ and X−, respectively, in Φ (N+⋅⋅⋅X−). Comparison of experimental hfc with calculated values yields estimates of the charge distribution (χ) and internuclear distance (R). In this procedure it is important to consider spin–orbital contributions to the observed hfc. Results are for XeF, R=4.70a0, χ=0.80. For KrF, R=4.00a0, χ =0.98. For XeCl, R=6.50a0, χ=0.955. These values are consistent with the relative sizes and electronegativities of the constituent atoms.