The scattering of slow electrons by polyatomic molecules. A model study for CH₄, H₂O and H₂S

Cross sections have been calculated for the scattering of slow electrons by water and methane molecules. A simple model is used: scattering is from a rigid molecule, exchange and polarisation effects are included in an approximate way, exchange by orthogonalising the scattered electron function to bound orbitals of the same symmetry and polarisation by using a potential correct at large distances but with an ad hoc short range cut-off parameter; the short range static interaction is, however, obtained from SCF target wavefunctions. Total, momentum-transfer and differential cross sections are given for CH₄. In this body-fixed approximation total cross sections are undefined for molecules with a permanent dipole moment such as H₂O and H₂S; results are given here for momentum-transfer and differential cross sections of H₂O. Possible negative-ion resonance states in H₂O and H₂S are discussed with reference to recent dissociative attachment and vibrational excitation experiments.