The Ramsauer minimum of methane

With a time-of-flight spectrometer the authors measured the electron total cross section of methane in the energy range 0.085-12 eV with particular attention to the Ramsauer minimum for which they determined a minimum cross section of 1.36(4)*10 -16 cm 2 at an energy of 0.40(2) eV. Both the cross section and the energy location are in excellent agreement with the early measurements of Ramsauer and Kollath but in significant disagreement with more recent measurements of Barbarito et al. (1979). By applying the formulae of the modified effective-range theory to the low-energy data up to 0.5 eV. The authors obtain momentum transfer cross sections in good agreement with the most recent analysis of swarm experiment data by Haddad (1985).