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.