Free-ion yields, electron mobilities and electron-ion recombination rate constants in liquid and solid isooctane and several other nonpolar compounds

Abstract

Free-ion yields ( G fi 0) in solid isooctane were determined by a new simple method which was a combination of the electric current measurement during irradiation of very low dose of 60Co γ-rays and the continuous measurement of thermostimulated current after the irradiation by applying d.c. high voltage to the solid isooctane. Electron mobilities (μ e) in the solid isooctane were determined by the free-ion yields and the measurement of peak electric current upon the X-ray pulse irradiation of a few nanoseconds width. In the liquid phase, however, G fi 0 and μ e were also measured by the usual charge clearing method and the decay curve analysis or peak current method, respectively. The effects of temperature from 26 to – 158°C and of phase change from liquid to solid on G fi 0, μ e and b (the most probable electron-thermalization length) are compared with those for neopentane, tetramethysilane, and cyclohexane. Some values of the G fi 0, μ e and b determined in liquid and solid isooctane are as follows: in liquid G fi 0=0.13 at -101°C, μ e =1.6 cm 2 V -1 s -1 at -99°C, b=103 A at -101°C; in solid, G fi 0=0.15 at -118°C, μ e =0 cm 2 V -1 s -1 at -118°C, b=104 A at -116°C. The values of apparent activation energy of μ e obtained by the Arrhenius plot are 0.049 eV in the liquid and 0.077 eV in the solid isooctane, respectively. As the results, it is concluded that in liquid and solid isooctane localized electrons play a main role in electron transport with somewhat larger contribution of quasi-free electrons than in liquid and solid cyclohexane and that the rather larger contribution of quasi-free electrons than in cyclohexane seems to relate to the variation in G fi 0 and b value with temperature and phase change. Electron-ion recombination reaction in some organic liquids and solids is also discussed.