Mobility of the electron in liquid and solid 3-methylpentane

Abstract

The authors have investigated the current of electrical conductivity I induced by a pulse of 2 × 10⁻⁷ s of high energy electrons in 3-methylpentane (3MP) over the temperature range 94–296 K. The determination of the drift mobility of the excess electron u is based on measurement of the amplitude of I in conditions in which the lifetime of the excess electron in 3MP τ ⪢ 2 × 10⁻⁷ s and the total number of free charges q generated in the course of one pulse. In liquid 3MP q was measured by integrating I and in solid 3MP by integrating the current of thermostimulated conductivity on heating the sample to melting point. At T = 296 K the value u = 0·22 cm² V⁻¹ s⁻¹ and agrees with the value obtained from measurements of the time of transit by the electron of the distance between electrodes d≈0·1 cm.

In the temperature interval from 94–296 K the value u monotonically changes from 10⁻⁸ to 0·22 cm² V⁻¹ s⁻¹. In the region of the melting point, the values of u in liquid and solid 3MP are much the same, whereas the activation energy changes from 0·14 to 0·4 eV on passing from liquid to solid 3MP. The activation energy of the mobility of the electron in solid 3MP is connected with the energy of the thermal release of the electron from the deepest structural traps.

Extrapolation of the function u(T) by the Arrhenius law with an activation energy of 0·4 eV gives the value u ≈ 10⁻¹⁵ cm² V⁻¹ s⁻¹ at 77 K which accords with the value obtained from measurement of the quasi-steady photo-conductivity and evaluation of the lifetime of the trapped electron in 3MP at 77 K.