Collisional $^{3}$He and $^{129}$Xe Frequency Shifts in Rb--Noble-Gas Mixtures

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 $\kappa _{0}$ that characterizes these shifts for Rb- $^{129}$Xe to be 493$\pm $31, making use of the previously measured value of $\kappa _{0}$ for Rb-$^{3}$He. This result allows accurate $^{129}$Xe polarimetry with no need to reference a thermal- equilibrium NMR signal.