We have used the Schwinger multichannel formulation [Takatsuka and McKoy, Phys. Rev. A 24, 2473 (1981)] to carry out ab initio studies of the effects of polarization on the cross sections for elastic scattering of electrons by the polyatomic molecule ${\mathrm{CH}}_4$ for collision energies from 7.5 down to 0.02 eV. Although the closed-channel expansion through which polarization effects are included in this approach is not fully converged, the resulting cross sections do show a Ramsauer-Townsend minimum between 0.1 and 0.2 eV, about 0.3 eV below where it is seen experimentally. Our static-exchange cross sections show no Ramsauer-Townsend minimum. At the higher energy of 7.5 eV, where polarization effects are less significant, the calculated differential cross sections are in excellent agreement with the measured values. Differential cross sections are also shown at 3.0 eV.

• Received 24 January 1989

DOI:https://doi.org/10.1103/PhysRevA.39.4312