Reactivity of charged species and cluster in supercritical fluids -Fast time-resolved spectroscopy and conductivity study-

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The most salient feature of supercritical fluids is the divergent increase of compressibility near the critical point, which is the governing factor of the behavior of charged species.1. Excess electrons in supercritical Xe and Kr are quasi-free and their mobility below the respective critical density can be accurately predicted by the deformation potential theory in terms of acoustical phonon scattering utilizing adiabatic compressibility2. The excimer (Xe_2^*) is produced by the recombination of Xe_2^+ with electrons. Xe_2^* can be quenched rapidly by molecular additives like ethane.3. Reaction rates of electron attachment to solutes increase sharply near the critical point due to stabilization of resultant ions by cluster formation. The rate constant for attachment to C_6F_6 reaches 1×10^<15>m^<-1>s^<-1>, however, that with oxygen is only about 2×10^<11> m^<-1>s^<-1>. The activation volume for the former reaction can be described by the continuum compressible model.4. Charge transfer reaction from C_6F_6^- ion to benzoquinone is diffusion-controlled and reaches a maximum 1.8×10^<11> m^<-1>s^<-1> at the density of isothermal compressibility peak.