Electron thermalization distances and free ion yields in dense gases and liquids-effects of molecular structure

Radiolysis free ion yields were measured as a function of electric-field strength in vapor/liquid equilibrium fluids of ethene, propene, cyclopropane, propane, n-butane and i-butane at 0.15c<3(d_c=critical fluid density). From these yields, secondary electron thermalization distances b_GP were estimated using the extended Onsager model. In the normal liquid at d/d_c>1.5, the effects of molecular shape gave b_GPd in methane>i-butane>ethane>propane>n-butane. The effect of pi -bonding gave n-butane>cyclopropane>ethene approximately propene; the permanent dipole of propene had negligible effect in the dense liquid. The conduction-band energy in supercritical fluids of n-butane, isobutane, n-pentane and isopentane was measured as a function of the fluid density. The conduction-band energy values in these fields show a density dependence that is related to their molecular structure. The correlation between the density dependence of conduction-band energy and of electron mobility is discussed in terms of the deformation potential theory.