Pairwise additivity in the nuclear magnetic resonance interactions of atomic xenon

Abstract

Nuclear magnetic resonance (NMR) of atomic ^129/131Xe is used as a versatile probe of the structure and dynamics of various host materials, due to the sensitivity of the Xe NMR parameters to intermolecular interactions. The principles governing this sensitivity can be investigated using the prototypic system of interacting Xe atoms. In the pairwise additive approximation (PAA), the binary NMR chemical shift, nuclear quadrupole coupling (NQC), and spin-rotation (SR) curves for the xenon dimer are utilized for fast and efficient evaluation of the corresponding NMR tensors in small xenon clusters Xe_n (n = 2–12). If accurate, the preparametrized PAA enables the analysis of the NMR properties of xenon clusters, condensed xenon phases, and xenon gas without having to resort to electronic structure calculations of instantaneous configurations for n > 2. The binary parameters for Xe₂ at different internuclear distances were obtained at the nonrelativistic Hartree–Fock level of theory. Quantum-chemical (QC) calculations at the corresponding level were used to obtain the NMR parameters of the Xe_n (n = 2–12) clusters at the equilibrium geometries. Comparison of PAA and QC data indicates that the direct use of the binary property curves of Xe₂ can be expected to be well-suited for the analysis of Xe NMR in the gaseous phase dominated by binary collisions. For use in condensed phases where many-body effects should be considered, effective binary property functions were fitted using the principal components of QC tensors from Xe_n clusters. Particularly, the chemical shift in Xe_n is strikingly well-described by the effective PAA. The coordination number Z of the Xe site is found to be the most important factor determining the chemical shift, with the largest shifts being found for high-symmetry sites with the largest Z. This is rationalized in terms of the density of virtual electronic states available for response to magnetic perturbations.