Ramsauer-Townsend minima in the electron-scattering cross sections of polyatomic gases: Methane, ethane, propane, butane, and neopentane

Electron drift velocities, w, as a function of temperature were measured and on the basis of these data, Ramsauer-Townsend (RT) minima were found in the cross section for momentum transfer, sigma _m, for all these gases. The position of the RT minimum and the magnitude of the corresponding sigma _m at the energy where the minimum occurs are 0.12, 0.14, 0.14, and 0.25 eV and 1.2, 3.0, 4.6, and 5.8*10^-16 cm² for ethane, propane, butane, and neopentane, respectively. The density dependence of the w for neopentane was also investigated. This latter investigation and similar ones in the literature on methane, ethane, and propane are discussed in connection with the observed RT minima and the mobility of thermal electrons in the low- and high-pressure vapours and the liquids of these compounds.