Epithermal Electron Ranges and Thermal Electron Mobilities in Liquid Aromatic Hydrocarbons

Radiolysis free ion yields were measured as functions of electric field strength and temperature in benzene, toluene, 1,2-, 1,3-, and 1,4-dimethylbenzene, 1,2,3-, 1,2,4-, and 1,3,5-trimethylbenzene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, pentamethylbenzene, hexamethylbenzene, naphthalene, and anthracene. Secondary electron ranges bGP were estimated from the yields. The density-normalized ranges bGPd were almost constant, 34−38 × 10−8 g/cm2, from benzene up to the tetramethylbenzenes, then increased to 47 × 10−8 in pentamethyl- and 52 × 10−8 in hexamethylbenzene. In naphthalene and anthracene the normalized ranges were 32 and ∼20 × 10−8 g/cm2, respectively. Electron mobilities in the liquids at 293 K, and their activation energies, expressed in (cm2/V s, kcal/mol) were: benzene (0.114, 7.4); toluene (0.063, 3.4); 1,2-dimethylbenzene (0.018, 4.4); 1,3-dimethylbenzene (0.057, 4.5); 1,4-dimethylbenzene (0.062, —); 1,2,3-trimethylbenzene (0.022, 4.8); 1,2,4-trimethylbenzene (0.035, 4.3); 1,3,5-trimethyl-benzene (0.17, 3.2); 1,2,3,4-tetramethylbenzene (∼0.02, 5). The mobilities reflect migration retarding influences of the aromatic ring and molecular asymmetry, and a slight ring-shielding effect of methyl groups that tends to enhance the mobility.