Phenomenology and scaling of electron scattering cross sections from ''almost spherical'' molecules over a wide energy range

Total cross sections for electron scattering on ''quasi spherical'' (CH4, SiH4, GeH4) molecules have been analyzed phenomenologically over a wide energy range. Regions, at low and high energies can be usefully represented by simple analytical formulae. Regularities associated with characteristic points such as the Ramsauer minima have been exposed. Comparison with other simple hydrides (NH3, H2O, H2S) allows the demonstration of a possible correlation between the maximum value of the total cross section and the bond length. Some points of contact with first-principles theory are noted and in particular the energy at which the maximum cross section occurs, is related to the occurrence of a partial wave resonance. In the absence of complete data for GeH4, prediction of characteristic points in the low energy cross section proves possible via the phenomenological analysis. Similarly, in the high energy regime, predictions of the cross section for SnH4 is made from data on the lighter molecules of the series, using non-relativistic Thomas-Fermi self consistent field scaling. (orig.)