Behavior of excess electrons in supercritical fluids-electron attachment

The behavior of excess electrons in supercritical ethane was investigated by measuring mobility and reaction rates. Mobilities were measured by means of a time-of-flight method at 306-320 K as a function of pressure. Mobility values decreased at all temperatures with increasing pressure, but showed a small minimum or a shoulder at the pressure where the compressibility χ_ϒ, has a peak. Electron attachment to CO₂, NO, pyrimidine and C₂F ₄ over the same temperature range was studied as a function of pressure. Both attachment rate constants k_a for NO and C ₂F₄, and equilibrium constants K(=k_a/k _d) for CO₂ and pyrimidine increased sharply at pressures of χ_ϒ peaks. Activation volumes V_a * and reaction volumes ΔV_r are very large and negative in the critical region. The volume change is mainly due to electrostriction around ions formed. The results are compared to volume changes predicted by a compressible continuum model