Radiolysis Free Ion Yields and Electron Ranges in Polar and Nonpolar Liquids: Fluoromethanes

Abstract

The free ion yields at zero applied electric field strength in the liquid fluoromethanes are Gfi0 in CH3F, 1.9 in CH2F2 and 1.1 in CHF3, all at 183 °K, and 0.07 in CF4 at 143 °K. Median ranges ymcd of the secondary electrons were estimated by fitting the electric field dependence of Gfi to a model equation: ymcd = 41 Å in CH3F, 39 Å in CH2F2 and CHF3, and 132 Å in CF4, at the above-mentioned temperatures. The average number of collisions, n, required to thermalize a secondary electron is about 64 000 in liquid Ar, 7 700 in CH4, 660 in C(CH3)4, 360 in CF4, 110 in C3H8, 44 in CH3F, 39 in CH2F2, 35 in CHF3, 17 in H2O, and 12 in CH3OH. The value of n with nonpolar molecules (up to neopentane in size) tends to decrease with increasing molecular complexity and with decreasing sphericity. Presence of a large dipole moment in the molecule decreases n further, and hydrogen bonds reduce n still more. Energy transfer between the electrons and rotational modes of the molecules appears to be important.