R. A. Holroyd, J. F. Wishart, M. Nishikawa, and K. Itoh
J. Phys. Chem. B, 107, 7281-7287 (2003). [Find paper at ACS Publications]
Abstract:
The results of an initial study of the pulse radiolysis of supercritical xenon are reported. In pure xenon, transients are formed which absorb broadly throughout the visible. These transients are assigned to excimer species, Xe2*, on the basis of lifetime and kinetic data. The formation of excimers by electron-ion recombination was time resolved by pulse-probe measurements. The excimers can be quenched by adding small amounts of ethane, which then facilitates detection of other transients by absorption spectroscopy. The added ethane also accelerates the thermalization of electrons and allows measurements of fast reaction rates of thermal electrons. Electron attachment to hexafluorobenzene occurs near the maximum rate at high pressures in xenon-ethane mixtures. The C6F6- anion formed absorbs with a maximum at 500 nm and disappears by second order kinetics. The mobility of this anion, as measured by conductivity, indicates sizeable clusters of solvent around the ion at all pressures, which are of maximum size near critical density. The rate of electron transfer from C6F6- to benzoquinone exceeds 1 x 1011 m-1 s-1 at most pressures. The rate maximizes near 62 bar at 21.4 C. A maximum at this pressure is predicted by diffusion. The maximum is related to the increase in cluster size around the anion, which occurs at this pressure.