The results of an initial study of the pulse radiolysis of supercritical xenon are reported. In pure xenon,
transients are formed that 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 sizable 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 × 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.