VERY-LOW ENERGY ELECTRON-SCATTERING IN SOME HYDROCARBONS AND PERFLUOROCARBONS

Low-energy scattering has been studied in CH4, C2H6, C3H6, C3H8, CF4, C2F6 and C3F8 in a transmission experiment using a synchrotron radiati on photoionization source. Backward scattering cross-sections have bee n determined over the energy range 10-175 meV. The variation of these cross-sections with electron impact energy has been analysed for non-p olar and weakly polar species using modified effective range theory, y ielding scattering lengths and low-energy limiting cross-sections. Rot ationally inelastic scattering cross-sections have been calculated for C3H6 and C3H8 using the first Born point-dipole approximation. Result s suggest that rotationally inelastic events contribute strongly to lo w energy scattering in C3H6 but only weakly in C3H8, reflecting the la rger dipole moment in C3H6.