In order to further elucidate the mechanism of electron solvation in polar liquids we have determined the rate of electron attachment to solute methanol aggregates, as a function of methanol concentration, in two nonpolar solvents. An infrared technique was used to measure the extent of methanol aggregation in the solutions. The methanol is present as monomer at low concentration but at high concentration forms aggregates which are mostly pentamers. The electron is unreactive with monomer but reacts at high rate with aggregate species. The reaction with pentamers is reversible, but the electron reacts irreversibly with larger aggregates. The results indicate a dynamic nature for the electron which can autodetach from shallow traps.

Publication costs assisted by Brookhaven National Laboratory Reaction rates of the electron, generated by X-ray ionization in various solvents, with a number of compounds which are known as good electron scavengers (e.g., SFg, XA). CCI4, CoHoBr, and trichloroethylene) have been determined as a function of temperature. The results are correlated with the quantity Vo, the energy of the electron in its mobile state, previously determined by photoelectric threshold measurements in the various solvents. The measured rate constants exhibit maxima for characteristic values of Vo, reminiscent of the resonant energy maxima in the dissociative attachment cross sections for electron reaction shown by the same molecules in the gas phase. Since Vq shifts toward more positive values with decreasing temperature, it is found that, for a particular solute, in a solvent having V0 lower than the value for the maximum electron-solute reaction rate, the reaction has a negative temperature coefficient. In solvents with higher V0 than corresponding to the maximum rate, the temperature coefficient of the reaction rate is positive. Thus the kinetics of these reactions appear quite different from those of ordinary chemical reactions. New data are presented on electron mobilities in various solvents, obtained incidentally in the course of the measurement of the rate constants. The relative reaction rates for quasifree electrons with various solutes in cyclohexane are in good general agreement with Schuler and Klein's values for relative reaction rates with transient "geminate" electrons.

The mobility of positive ions was measured in supercritical ethane, xenon, and carbon dioxide as a function of pressure at several temperatures. In supercritical CO2 the mobility of negative ions was also measured. Radii of the moving clusters were calculated with a hydrodynamic compressible continuum model that takes the enhancement in density and viscosity near the ions into account. The results show that positive ions move with a large solvation shell. Changes in size of this shell occur as a function of temperature and pressure. The largest radii at each temperature are found to occur at the pressure corresponding to the maximum in the isothermal compressibility. For positive ions the first solvation shell is totally filled under all conditions.

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Publication costs assisted by Brookhaven National Laboratory Single-photon ionization quantum yields are reported for tetramethyl-p-phenylenediamine (TMPD) as a function of wavelength and temperature in various dielectric liquids. At 23°the maximum quantum yield is observed at short wavelengths and is 0.07 in tetramethylsilane, less in cyclopentane, 2,2,4-trimethylpentane, and 2,2-dimethylbutane, and ~10~B in n-alkanes (C4-C14). In the n-alkanes there is a marked temperature effect on the quantum yield. For branched hydrocarbons the effect of temperature is less pronounced. The variation in yields with temperature is accounted for by the Onsager equation; this suggests that (ion pairs) is close to unity and that electrons and cations separate characteristic distances in each liquid. These distances range from 31 Á in n-hexane to 106 Á in tetramethylsilane. Wavelengths for ionization onsets depend on the energy of the excess electron (Vo) in the solvent and are used to evaluate this quantity for 18 different liquids. The results also suggest that V0 shifts toward more positive values at lower temperatures.