SCATTERING OF THERMAL ELECTRONS BY POLAR MOLECULES

Mean scattering cross sections and drift velocity data for thermal electrons in 34 polar molecules in the pure form and 4 in mixtures with ethylene are presented and discussed. The electric molecular dipole moment μ ranges from 0 to about 4·1 debye. The general conclusion is that the point-dipole Born approximation calculation of Altshuler is in better agreement with experiment than the exact calculation of Mittleman and von Holdt. Further, the experimental cross sections are higher than those predicted by Altshuler for all μ ≲ 2·4 debye and smaller when μ ≳ 2·4 debye, while their behaviour at and around the minimum dipole moment μmin required to bind an electron is complicated. The overall dependence of the experimental cross sections on μ indicates the possible effect of the binding of an electron to a molecule (when μ > μmin) and the possible effect of a potential resonance as predicted by Takayanagi and Itikawa.