Rates and energy of reactions of charged species in supercritical xenon

Pulse radiolysis was used to study the rates of several electron transfer reactions in supercritical Xe over a range of pressures. The rates of electron attachment to oxygen and 4,4′-bipyridine were also studied; the latter reaction is sufficiently fast to compete with electron-ion recombination, which is very fast in supercritical Xe. Electron transfer from 4,4′-bipyridine anion to benzoquinone is diffusion controlled. A peak in the rate is observed in the pressure region of maximum compressibility as expected for diffusion control. The rates of electron transfer from 4,4′-bipyridine anion and from hexafluorobenzene anion to O2 are an order of magnitude slower than expected for diffusion. The energetics of these reactions is discussed.