Electron Mobilities and Ranges in Liquid Hydrocarbons: Cyclic and Polycyclic, Saturated and Unsaturated Compounds

Abstract

Penetration ranges bGp of secondary electrons into 21 X-irradiated liquids were estimated from measured free ion yields. The density normalized ranges bGpd are independent of temperature. Increasing the molecular symmetry by creating one or more cycles in the molecule causes the normalized range to increase, provided that the amount of bond distortion due to strain remains small. Ranges are smaller in compounds that contain strained rings. Energy transfer from the secondary electrons to the molecules is enhanced by the presence of distorted bonds in the molecules. The ranges in olefins are affected by the same factors as those in saturated hydrocarbons, with the addition of a contribution of transient negative ion states to the energy transfer processes. Shielding the double bond by methyl groups is not effective; the effect of the added methyl groups on the molecular symmetry is a more important factor. The magnitude of the energy transfer interaction is an inverse function of molecular symmetry.The general correlation between bGp and thermal electron mobilities ue in liquids contains significant variations within it. For a given value of bGp, ue in different liquids increases in the order n-alkane < cycloalkane < cycloalkene < 1,4-cyclohexadiene or benzene. Arrhenius plots of ue in cyclic olefins curve downwards at low temperatures, due to the formation of a deeper trapped state of the electron. The trap is deepest in 1,4-cyclohexadiene (21 kcal/mol) and is attributed to an equilibrium between solvated electrons and anions at temperatures below about 280 K.