Kengo Itoh

Photoconductivity threshold of supercritical xenon fluids doped with anthracene as a function of fluid density

Abstract The photoconductivity threshold energy I f of supercritical xenon fluids doped with anthracene was measured as a function of fluid density N from 0.03 × 10 21 to 7.5 × 10 21 cm −3 . For high densities ( N ⩾ 7 × 10 21 cm −3 ), I f values were well described by the equation I f = I g + V 0 + P , where I g is the gas-phase ionization potential of anthracene, V 0 the conduction band energy in the xenon fluids and P the polarization energy of an anthracene positive ion. The value of the ionic radius, 0.325 nm, used for the calculation of P is derived from literature data on I f in non-polar liquids. The deviation of measured I f values from the above expression is discussed.

ELECTRON TRANSPORT IN O- AND M-XYLENE UNDER HIGH PRESSURE

The electron drift mobility (μ) was measured by a time‐of‐flight method in pure liquid o‐ and m‐xylene under high pressures up to 300 MPa, and in the temperature ranges from 15 to 120 °C and 0 to 100 °C, respectively. In both liquids μ increases in the lower pressure region at lower temperatures. At higher pressures μ decreases gradually with pressure at all temperatures studied. The pressure dependence of μ was interpreted in terms of a two‐state model and a hopping model. When μ increases with pressure this interpretation leads to a positive volume change upon introduction of electrons into the liquid, showing electrons reside in cavities of radius 0.31 to 0.32 nm, whereas in the high pressure region electron attachment to xylene molecules occurs, accompanied by hopping of electrons between molecules.

Electron mobility in liquid n‐hexane/2,2‐dimethylbutane mixtures under high pressure

The effect of pressure on the electron mobility in mixtures of n‐hexane and 2,2‐dimethylbutane was studied over the whole concentration range. The variation of mobility with pressure is discussed in terms of a two‐state model, and provides information on the volume changes occurring on localization. The observed volume changes are interpreted as the difference between the cavity volume and the electrostriction volume of the localized electron.

Conduction band energy V0 in dense fluids of n- and iso-butane

Abstract The conduction band energy V 0 in n - and iso-butane has been measured as a function of the density N in the liquid phase and the supercritical state. Molecular-shape effects on the shape of V 0 ( N ) curves are discussed.

Mobility of excess electrons in hexamethyldisiloxane and bis(trimethylsilyl)methane

Abstract The mobility of excess electrons in bis(trimethylsilyl)methane is 63 cm 2 /V s, and in hexamethyldisiloxane 22 cm 2 /V s. For these and related silicon-containing compounds, the mobility is greater than for those alkanes which have comparable free-ion yields.

Effect of high pressure on free ion yields for liquids exposed to X-rays

The effect of pressure on the free ion yield is reported for six nonpolar liquids exposed to X-rays. The free ion yields are determined from the magnitude of the electronic signal following an X-ray pulse. Changes in the free ion yield with pressure are largely uncorrelated with changes in the electron mobility. The mean thermalization range, b, inferred from the free ion yields, decreases with increasing pressure in all liquids, and the product of the range times the density remains quite constant with pressure.

Volume and entropy changes in electron attachment reactions: Butadiene in 2,2-dimethylbutane

Abstract The equilibrium: e − + 1,3- butadiene ⤦ butadiene − is observed in dimethylbutane at pressures 1500 bar. Both the forward (attachment) and reverse (detachment) rate constants are measured by pulse conductivity. By extrapolation it is estimated that the equilibrium constant at 1 bar and 20°C is approximately 10 molal−1. The reaction volumes range from −95 to −122 cm3/mol. These volumes are attributed to the volume of electrostriction by the butadiene anion. The electrostriction volumes, calculated with a model which includes a glassy shell of solvent molecules, are in good agreement with experiment.

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

The excess electron mobility in supercritical n-, iso- and neopentane was measured isothermally as a function of density. The density-normalized mobility μN in all three isomers goes through a minimum at a density below the respective critical densities, and the mobility is quite temperature-dependent in this region, then goes through a minimum. The μN behavior around the minimum in n-pentane is well accounted for by the Cohen-Lekner model with the structure factor S(K) estimated from the speed of sound, while that in iso- and neopentane is not.

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.

Reaction of electrons with CO/sub 2/ in nonpolar solvents

The rates for the reaction CO/sub 2/+e/sup -/ to or from CO/sub 2//sup -/ were determined in liquid 2.2-dimethylbutane (DMB) and isopentane (i-P) as a function of temperature. In 2,2-DMB both forward and reverse rates were measured over the 14-45 degrees C range, while in i-P only the forward reaction was observed over 0-73 degrees C. The rates and equilibrium constants are compared with those determined in other solvents, and the factors which influence these quantities in solutions are discussed. CO/sub 2/ was found to be highly reactive in 2,2-DMB and i-P solutions. The reactivity in solution is understood in terms of energetics. Equilibrium for the reaction in solution is explained in terms of the total energy, given by the difference between the ground state energy of electrons in the solvent and the polarization energy due to the anion formed by electron attachment.<<ETX>>