Ulrich Sowada

Excess electrons and positive charge carriers in liquid ethane

Measurements of excess electron drift velocity as a function of the electric field were carried out up to field strengths of 280 kV/cm at temperatures from 111 to 216°K. Low field mobilities were obtained and at higher field strength the drift velocity increased more than proportionally with the field. The data are discussed on the basis of the trapping model, and thermally activated hopping is assumed for the motion. The jumping length as a function of the temperature was obtained from the high field data. The positive charge carrier seems to be of ionic nature and the mobility follows Waldens rule.

Laser photodetachment of electrons from O2− in nonpolar liquidsa)

The wavelength dependence of the photodetachment cross section of electrons from O2− in liquid tetramethylsilane, 2,2‐dimethlypropane, 2,2,4‐trimethylpentane and argon was measured from the conductivity change induced by a short laser pulse. The O2− was generated by exposing a solution of O2 to a pulse of 2 MeV x rays just prior to the laser pulse. Comparison with gas phase results from the literature shows that the threshold law is the same in the two phases, and that the size of the cross section is similar at comparable excess energies. However, the thresholds are shifted from the infrared in the gas phase to the visible region in solution. The observed values are: Eth=2.08, 2.02, 2.55 eV in tetramethylsilane, 2,2‐dimethylpropane, and 2,2,4‐trimethylpentane at 296 K, respectively, and 2.32 eV in tetramethylsilane at 200 K. The major energy term causing this shift is the solvation energy of O2−. If this is described by Born’s equation the effective radius of O2− is 1.54±0.02 A in the hydrocarbons and te...

Electron mobility in supercritical propane as a function of density and temperature

The mobility of excess electrons in supercritical n‐ and isobutane was measured as a function of density at several temperatures. The density‐normalized mobility μN in both isomers goes through a minimum at a density below the respective critical density and the mobility is quite temperature dependent in this region, then goes through a maximum above the critical density where it is rather insensitive to temperature. The minimum in isobutane is not reproduced by the Cohen–Lekner equation with the structure factor S(K) estimated from the velocity of sound, while it is well accounted for by the model in n‐butane. This and other characteristics in the mobility behavior for n‐butane are typically those of nonspherical hydrocarbons such as ethane and propane, but are intermediate between spherical and nonspherical hydrocarbons for isobutane.

Comment on the paper ‘‘The role of shallow traps on the mobility of electrons in liquid Ar, Kr, and Xe,’’ by G. Ascarelli, J. Chem. Phys. 71, 5030 (1979)

The electron drift velocity in liquid Ar, Kr and Xe is furthe discussed. It is proposed that the electron transport occurs via shallow traps. Some experimental evidence is cited for the presence of hot electrons in liquefied rare gases. (AIP)