Behavior of charged species in supercritical heavy rare gas fluids

Electron mobilities were measured in supercritical (SC) Xe and Kr as functions of pressure and temperature. Ion mobilities, reaction rates of electrons with C6F6, O2 and pyrazine were also measured in SC Xe. Electron mobility is strongly field-dependent and the low-field mobility μe exhibits a deep minimum at a density just below the critical density. A deformation potential model of the acoustic phonon scattering type can reproduce μe change in SC Xe and Kr quantitatively. From positive ion mobility values, a hydrodynamic compressible continuum model indicates that the cluster radius goes to a maximum, 1 nm, at 291 K at the pressure of the isothermal compressibility, χT, peak. The rate constant for the reaction C6F6+e−→C6F6– sharply increases up to nearly 1015 molal s−1 in this pressure region. Pyrazine was found to form neutral clusters in SC Xe prior to electron attachment. These and other data are compared with the observation made in SC ethane.