Electron scattering by methane using exact exchange

Eigenphase sums and cross sections have been calculated for the scattering of slow (<20 eV) electrons by methane molecules in a full exchange approximation. Results agree well with the previous work of Lima et al. (1985). Comparison is made with the local free-electron-gas exchange approximations in the A 1 and T 2 scattering states and it is shown that the 'asymptotically adjusted' model is better than the 'Hara' model (1967) except at very low energies in the A 1 state. Cross sections have also been calculated using full exchange and the polarisation potential introduced by Jain and Thompson. Comparison with experiment is good.