Vibrational excitation of methane by slow electrons revisited:: theoretical and experimental study

We have calculated and measured differential and integral cross sections for vibrationally inelastic scattering of electrons by methane molecules. The calculations were carried out using the discrete momentum representation (DMR) method. We solved the two-channel Lippmann-Schwinger equation in the momentum space. The interaction between the scattered electron and the target molecule is described by the exact static-exchange potential. Correlation-polarization forces were included by a simple local density functional theory potential of Perdew and Zunger (1981 Phys. Rev. B 23 5048). The cross sections calculated in this way agree very well with our measurement and with other more recent experimental data, but are larger than some older experimental and theoretical results.