Local approximations of exchange interaction in electron-molecule collisions: The methane molecule

The interaction of slow electrons (collision energies up to about 20 eV) with polyatomic targets is examined for the specific case of the methane molecule in order to study the effect on total cross sections of various local approximations for the exchange interaction between bound and continuum electrons. It is found that the tail of such an interaction, outside the 'hard-core' region of the static potential, plays an important role at very low collision energies and ultimately controls the correct appearance of the experimentally found Ramsauer-Townsend (RT) minimum in the integral elastic cross section. Very good agreement between computed and measured values for the cross sections is found when using the modified semiclassical exchange approximation (MSCE) proposed. The broad resonance, which appears at experimental energies of around 8 eV, is also satisfactorily reproduced by the present methods.