CollisionalHe3andXe129Frequency Shifts in Rb–Noble-Gas Mixtures

Abstract

The Fermi-contact interaction that characterizes collisional spin exchange of a noble gas with an alkali-metal vapor also gives rise to NMR and EPR frequency shifts of the noble-gas nucleus and the alkali-metal atom, respectively. We have measured the enhancement factor κ0 that characterizes these shifts for Rb-129Xe to be 493±31, making use of the previously measured value of κ0 for Rb-3He. This result allows accurate 129Xe polarimetry with no need to reference a thermal-equilibrium NMR signal.

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

“…This figure was arrived at by using the experimentally feasible Xe nuclear spin polarization P Xe = 0.32 in the same number density and temperature range as above but now with our calculated value for the second virial coefficient of the Xe hyperfine coupling A iso Xe,1 . The corresponding interaction-induced changes of A iso Xe due to the other gas species present in SEOP experiments, He and N 2 , might also play a role [11,26]. However, as no hyperfine interactions take place between these species and xenon, their effect is inevitably smaller than the effect of rubidium.…”

“…The 129 Xe NMR and EPR frequency shifts occurring in SEOP experiments have been observed for years [10,11,13]. A major advance in the detection of the 129 Xe NMR frequency shift in the Rb-Xe gas mixture has recently taken place, leading to a reevaluation of the value of the enhancement factor [11].…”

“…A major advance in the detection of the 129 Xe NMR frequency shift in the Rb-Xe gas mixture has recently taken place, leading to a reevaluation of the value of the enhancement factor [11]. Despite the growing knowledge and number of experimental applications of HP techniques, only a handful of first-principles modeling studies have been performed in the field of HP physics [14][15][16], mainly discussing the role of the anisotropic HFCC as a limiting relaxation factor in HP experiments [9].…”

“…The polarization exchange occurs due to the magnetic hyperfine interactions between the electron spin of the alkali metal and noble-gas nuclear spin. These interactions can be represented by the so-called enhancement factor κ [10,11] that is directly related to the observed frequency shifts in both the NMR and electron paramagnetic resonance (EPR) regimes. However, the enhancement factor can also be evaluated microscopically using first-principles quantum-mechanical electronicstructure calculations.…”

“…Here, we use state-of-the-art electronicstructure calculations to provide theoretical estimates of the 129 Xe HFCC in the Rb-Xe dimer as a function of the internuclear separation. This parameter, averaged over the corresponding Rb-Xe potential-energy curve (PEC), is the essential factor contributing to the NMR and EPR frequency shifts [11] in the gaseous conditions characteristic of SEOP experiments. We report a highly electron correlated Rb-Xe PEC using the relativistic pseudopotential technique, which can be used, in addition to SEOP studies, in the theoretical description of the bonding characteristics in weakly bound van der Waals molecules [18,19].…”