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 /spl chi//sub /spl Upsi//, has a peak. Electron attachment to CO/sub 2/, NO, pyrimidine and C/sub 2/F/sub 4/ over the same temperature range was studied as a function of pressure. Both attachment rate constants k/sub a/ for NO and C/sub 2/F/sub 4/, and equilibrium constants K(=k/sub a//k/sub d/) for CO/sub 2/ and pyrimidine increased sharply at pressures of /spl chi//sub /spl Upsi// peaks. Activation volumes V/sub a/* and reaction volumes /spl Delta/V/sub 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.