Electron Thermalization in Dense Gases and Liquids: Effect of Conduction Band Formation

The yields of free ions produced by X-radiolysis were measured as functions of applied electric field strength in coexisting vapors and liquids of spherelike (methane) and rodlike (ethane) molecules at densities 0.14¿ d/dc¿2.8 (dc is that of the critical fluid). The Onsager model was used to estimate the electron thermalization distances bGP. The density normalized distance bGPd is inversely related to the energy loss cross section of epithermal h~al ("\´ 0.1 to 1 eV) electron/ A~/ dc,% 0.14 in the low density gas, where the molecules are too far apart for a conduction band to form, bGPd = 5.5x10-6 kg/m2 in both methane and ethane. In denser gases at d/dc¿0.3, bGPd increases slightly, due to mulitbody effects. A drastic change occurs with conduction band formation at d/dc> 1.0; bGPd in liquid methane increases to ~4 times the value in liquid ethane. Epithermal energy losses are ~4 times less efficient in the conduction band formed by spherelike methane molecules than in that formed by rodlike ethane molecules.