Positron scattering from methane

We report on measurements of total cross sections for positron scattering from the fundamental organic molecule methane (CH ₄). The energy range of these measurements was 0.1-50 eV, whereas the energy resolution was ∼100 meV when our Ni moderator was used and ∼260 meV when the W moderator was employed. To assist us in interpreting these data, Schwinger multichannel calculations were performed at both static and static plus polarization levels of approximation for elastic positron scattering from 0.001 to 10 eV. These calculations are found to be in quite good qualitative agreement with our measured data, and they clearly educe the crucial role played by the target polarization in the low energy positron-CH ₄ scattering dynamics.