Collisions of electrons with polyatomic molecules: Electron-methane scattering by the complex Kohn variational method

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Abstract
The complex Kohn variational method, which is an anomaly-free algebraic variational procedure, is implemented for the case of collisions of electrons with polyatomic molecules. The complex Kohn method requires only Hamiltonian matrix elements and, in this formulation, does not require any exchange matrix elements involving continuum functions. Direct matrix elements of the scattering potential(s) which involve continuum functions are evaluated by an adaptive three-dimensional quadrature scheme. The entire procedure is applied to elastic electron-methane scattering at the static-exchange level and proves to be both efficient and accurate. No Ramsauer-Townsend minimum is found at low energies, and it is concluded that this feature of the experimental cross section cannot be described theoretically without the inclusion of target polarization.