Chapter 2: The Xenon Chemical Shift and Chemical Shift Anisotropy

The Xe intermolecular shielding tensor is a steep function of distance and the configuration of the neighboring atoms or molecules. This sensitivity of the Xe shielding function is the basis for the exquisite sensitivity of the Xe atom as a probe of its environment. The expected isotropic chemical shift observed under conditions of isotropic averaging and the chemical shift anisotropy that is characteristic of Xe confined in anisotropic environments in the solid state are shown to be easily understood and predicted. Quantum mechanical molecular level interactions determine the (a) sorption thermodynamics, (b) the Xe exchange dynamics, and (c) the instantaneous shielding at a Xe nucleus arising from the electronic environment formed by all the rest of the atoms, including other Xe atoms. The average Xe chemical shift is a weighted average of the shielding function (c) with weighting factors determined by (a) and (b). We demonstrate how an understanding at a fundamental level helps us to elicit the desired detailed information about the physical system from information encoded by Xe into its chemical shift in the gas phase, in solution and in confinement in solution and in the solid state.