Temperature-dependent chemical shift in the aqueous solution of xenon

Abstract

At standard pressure, the chemical shift of Xe-129 in an aqueous solution of xenon exhibits a maximum as a function of temperature at 311 K, which is in contrast to the well-known density maximum of water at 277 K. In the present work, this phenomenon is studied by means of a molecular dynamics simulation, where the xenon chemical shift is computed quantum-chemically for snapshots of the simulation trajectory. Also, a simple semianalytical model is developed in which the water around the xenon atom is interpreted to form a shell of uniform density. Both approaches are found to be able to qualitatively reproduce the maximum. In addition, the chemical shift in the semianalytical model is seen to result as a product of the local water density around the xenon and a term corresponding to the xenon-water collision energetics. The latter term can be seen to shift the location of the maximum up in temperature, as compared to the temperature of maximum density.