Chemical shifts in paramagnetic gas mixtures

Abstract

Analysis of the large ¹²⁹Xe nuclear magnetic resonance shifts induced by gaseous O₂ and NO indicates that they arise from a ‘contact-overlap’ mechanism. Overlap of the Xe (5s) and the O₂ (πg*) or NO (π*) orbitals is the major contributor to the spin density at the Xe nucleus. The shift is an average over all configurations with a Boltzmann-type weighting determined by the intermolecular potential. The calculated shift is sensitive to the wavefunctions used for Xe and O₂ and to the intermolecular potential. Predictions of the temperature dependence of the shifts are made. If the overlap is accurately known (as for H₂-O₂ or ³He-O₂) the shift could yield a valuable new means of determining intermolecular potentials. The N.M.R. shift is related to the hyperfine pressure shifts of the paramagnetic species and to its change of g-value.