Electron and nuclear spin polarization in Rb-Xe spin-exchange optical hyperpolarization

Abstract

Spin-exchange optical hyperpolarization of ¹²⁹Xe gas enhances the signal-to-noise ratio in nuclear magnetic resonance experiments. The governing parameter of the Rb-Xe spin-exchange process, the so-called enhancement factor, was recently reevaluated experimentally. However, the underlying hyperfine coupling and atomic interaction potential as functions of the internuclear distance of the open-shell Rb-Xe dimer have not been accurately determined to date. We present a piecewise approximation based on first-principles calculations of these parameters contributing to the NMR and EPR frequency shifts in the low-density Rb-Xe gas mixture of relevance to hyperpolarization experiments. Both Rb electron and ¹²⁹Xe nuclear spin polarizations are estimated based on a combination of electronic-structure calculations, observed frequency shifts, and an estimate of the Rb number density. Finally, an expression for the enhancement factor in terms of modern electronic-structure theory is obtained.