We present a formulation for low-energy positron-molecule collisions based on the Schwinger multichannel method (SMC) which was previously adapted for electron-molecule scattering. We have preserved very important features of the SMC such as its ability to deal with electronically inelastic scattering and its applicability to molecular targets of arbitrary geometry. Our implementation also allows for the inclusion of a substantial number of closed electronic channels to represent polarization effects, which are very important at low impact energies. As an application, to illustrate the form with which polarization is represented in this formulation, we have calculated elastic integral and differential cross sections for ${\mathit{e}}^{+\mathrm{-}}$${\mathrm{H}}_2$ and ${\mathit{e}}^{+\mathrm{-}}$${\mathrm{CH}}_4$ collisions. We included all possible single-particle excitations from the target and found substantial disagreement with respect to model potential calculations and attenuated-beam experimental data. We discuss possible reasons for these discrepancies.

• Received 4 September 1992

DOI:https://doi.org/10.1103/PhysRevA.47.3976