The validity of diffusion concepts for describing the kinetics of recombination of an excess electron in liquid hydrocarbons

Abstract

A comparison has been made of the experimental and calculated relative values of the efficiency of capture by the acceptor molecule of an electron generated by ionizing radiations (the α coefficient in Hummel's theory) in liquid hydrocarbons at room temperature; pentadecane, n-hexane, iso-octane and neopentane. For the experimental determination of the values of α the authors used the measurements of luminescence induced by a pulse of fast electrons in solutions of pyrene (10¹⁵−10¹⁶ cm⁻³) in hydrocarbons. Calculation of the values of α for the diffusion description of the process of recombination of an electron is based on the relation: α≈K_Sr_m^3/u, where K_S is the rate constant of capture of an electron by the molecule of pyrene; u is the drift mobility of the electron; r_m is the most probable distance of thermolysation of an electron. The values of K_S and u for pentadecane and neopentane were determined by investigation of the electrical conductivity induced by a pulse of fast electrons in solutions of pyrene; for K_S and u in the case of n-hexane and iso-octane and also for r_m the published data were used. It is shown that while for hydrocarbons with relatively low mobility of the electron the calculated and experimental values of α agree, for the hydrocarbon with the highest mobility of the electron (neopentane) use of diffusion concepts for the calculation gives an overstated value of α.